Capsicum baccatum (pepper)

Sporophytic chromosome count for the species is 24 (IPCN Chromosome Reports, 2014).

The flowers are protogynous, but readily self pollinate. In the field, high rates of outcrossing (up to 90%) can occur with insect pollination. Capsicum exhibits no inbreeding depression. The stigma is positioned slightly below the level of the anthers or exserted slightly beyond, in which case the chances for cross-pollination are greater. Pepper breeders and seed producers use caution when producing a seed crop to prevent uncontrolled cross-pollination. The flowers are normally solitary in the axils of the branches, with the occasional cluster type that causes multiple flowers to form at a node. Many of the wild species have multiple flowers per node. There are two to four or more locules within the fruit. The locules are separated by the placentae where the capsaicinoids are produced. The outer wall, or pericarp, is fleshy and varies in thickness. It consists of a very thin cuticle, five to eight compact layers of small collenchyma cells that are cutinized during maturation and provide a tough, colourless, epidermal layer or skin. The growth of the fruit in the early stage consists of rapid cell multiplication; in the later stages growth is chiefly by enlargement of the cells already formed.

Capsicum plants grow best at low-to mid elevations with 7-8°C, annual rainfall of 300-4600 mm and well-drained, sandy or silt-loam soil with pH of 4.3-8.7 (Basu and De, 2003; Ravishankar et al., 2003). FAO reports optimal annual rainfall levels for C. baccatum var. pendulum to be 600-1250 (absolute 500-1500) and temperature absolutes of 15-32°C, with the ability to grow in climatic zones ranging from tropical wet or wet and dry, to subtropical humid, dry summer, or dry winter (FAO EcoCrop, 2014). In Bolivia, C. baccatum grows in dry to montane forest and dry valleys at altitudes of 0-2000 m (Bolivia Checklist, 2014), while in Paraguay, the species occurs in low and high-altitude forests (Paraguay Checklist, 2014).

The two most common abiotic disorders are blossom-end rot and sunscald. Blossom-end rot occurs when the plant is unable to translocate adequate calcium to the fruit, a condition caused by fluctuating soil moisture (drought or over watering), high nitrogen fertilization or root pruning during cultivation. This disorder first appears as a water-soaked area on the fruit. The tissue near the blossom end of the pods has a brown discoloration. Unlike tomatoes, blossom-end rot is never actually at the blossom end, but more on the side of the fruit. Sunscald is caused by intense sunlight on fruit that had been growing in the plant’s shaded canopy. The smaller-podded varieties with erect fruit are not as susceptible to sunscald as the large-podded varieties, such as bells and New Mexican pod types.

Another common disorder is flower drop. Flower buds, open flowers and immature pod drop are caused by a variety of conditions. Heat stress, insufficient water and excessive or deficient nutrient levels have been reported as casual agents.

Stip or blackspot is a newly discovered abiotic disorder on pepper fruit. Stip causes grey-brown to greenish spots on the fruit, most noticeable on red fruit that matures in the autumn. The disorder manifests itself when peppers are grown under cooler temperatures and associated with a suspected calcium imbalance, and possible shorter day-length. Stip can occur in the interior tissue of fruit as well as on the external surface. The disorder only affects some pepper cultivars, so the best control is to plant resistant cultivars.

Oedema appears as numerous small bumps on the lower side of the leaves, and sometimes on the petioles. The cause is most likely to be over-watering, although high humidity can also contribute to the problem. Control measures include reduced watering and better air circulation around the plant.

Inadequate phosphorus produces weak plants with narrow, glossy, greyish-green leaves. The red or purple colouration of stems and leaves often associated with phosphorus deficiency does not develop on peppers. Fruit produced on pepper plants deficient in phosphorus are shorter. Low levels of potassium produce a bronzing condition on the pepper leaves, followed by necrosis and leaf drop. Magnesium deficiency is characterized by pale-green leaf colour followed by interveinal yellowing, leaf drop, small plants and undersized fruit. Magnesium deficiency generally occurs when pepper plants are grown on acidic, sandy soils in areas of high rainfall. Compared with soil applications, spray applications of magnesium and other minor elements are more effective and have a more rapid (but shorter-lived) effect.

Principal sources: Janick and Paull (2008); Bosland and Votava (2012)

Ideally, peppers should not be planted in the same field more than once every 3-4 years and, in the intervening years, the crops grown in the field should be non-solanaceous crops such as wheat, brassicas, maize, lucerne and legumes. The use of raised beds is a common cultural practice for pepper production, but it is not always essential. Factors such as soil type, soil salinity, cultivation methods, type of irrigation, and drainage need to be considered when deciding on whether or not raised beds will be used. Most commercial pepper production in the USA occurs on 15-20 cm raised beds to promote drainage. Beds can be various sizes but are commonly 122 cm wide and 183 cm centre-to-centre. Most peppers are grown on soil that is highly prepared with tillage work. The soil can be tilled in a number of ways and rotovators can create a smooth bed if there is little residue. In some cases, fields are ploughed, particularly if heavy residue must be incorporated, tilled, and the beds reshaped. Cultural factors are implicated as being more important in seedling survival rate than the physical, mechanical transplanting operation. The optimum soil pH is 6.0-6.5, if found to be lower than this a suitable liming material should be applied during site preparation at a rate of 30 g/m².

Improved methods of transplant production and handling have increased survival rates of relatively young transplants, and field pruning to control growth of large pepper transplants is seldom used. Staking of field grown plants has been used to improve yield but its effectiveness depends on N and water supply.

Young transplants naturally branch into two or occasionally three shoots. This occurs after the fifth to the eighth node. Under greenhouse conditions, plants are normally trained to two stems each. Peppers are brittle so they need adequate support, the most common support system being string. Strings are tied to the stems and the string is supported from overhead wires 2.5-3.0 m above. At about 4 weeks after planting, two of the strongest shoots are selected. Stems are tied to the strings supported from the overhead wires. The stem requires twisting around the string stock wire every 10-14 days. Failure to maintain regular pruning can result in lost production and reduced plant growth rates. Ideally, a pepper plant will set one fruit for every two leaves. When the lateral branches have four leaf axils above the first fork, the flowers are allowed to set. Misshapen and diseased fruit are removed as soon as possible. Side shoots are removed as soon as possible, allowing for better light penetration and larger flower development. The option of leaving more leaves per shoot is possible when light intensity is high, the additional leaves will prevent sunscald of the fruit. The first flower on the young pepper plant is removed. The removal is important because if a fruit sets, early extension growth is reduced and the plant will have a stunted habit with a poorly developed fruit.

Pepper plants have extensive root systems that are moderately deep-rooted with taproots reaching a depth of more than 1 m. Although peppers are generally drought resistant, intermittent periods of moisture, and/or nutritional stress can dramatically reduce plant growth, fruit size, and yield. Flowers and young fruit may abscise if water stress occurs during flowering. The water requirements for pepper production range from 400 to 1000 mm. The broad range reflects differences in cultivar and environmental conditions. The general irrigation recommendation of a minimum of 2.5 cm/week applies to pepper. On sandy soils, more water may be required. Drip irrigation provides uniform and efficient water application directly to the root zone. Furrow irrigation may be an option in areas where water is plentiful and the infrastructure supports it.

Peppers do not remove as many nutrients from the soil as tomatoes. When both the plants and fruit are considered, a pepper crop will remove approximately 134 kg N, 13.4 kg P, 134 kg K/ha. Fertilization should be performed in response to both soil and foliar testing to ensure that only the nutrients needed by the plant are applied. Peppers respond to N fertilization, which is often applied prior to transplanting by row banding. Depending on testing results, a second application of N may be applied again at first flowering. However, excessive N wastes costly fertilizer, may damage the environment, and favours vegetative growth while inhibiting reproductive growth, thus delaying maturity and decreasing marketable yields.

Fertigation in the field is common with plasticulture pepper production. Phosphorus fertilizer may be banded at transplanting because of limited solubility and the rest of the nutrients fertigated during the season in response to tissue or petiole sap mineral analysis. A liquid starter solution high in P is often applied to the root zone at transplanting to stimulate early growth. A standard starter solution recipe may consist of 1.5 kg/200 litre of 8N-24P-8K or 10N-52P-17K, with 118 ml applied to each transplant.

Field grown peppers are often produced with some type of mulch and the most common artificial mulching material is plastic (usually polyethylene) film. Black plastic mulch typically improves pepper yield compared to bare soil although negative effects may occur under high ambient temperatures. The main advantages are increased early yields, improved moisture retention, inhibition of weeds, reduced fertilizer leaching, decreased soil compaction, fruit protection from soil deposits and soil microorganisms, and facilitation of fumigation.

Weed control has to start as pre-emergence treatment by cultivating or by using herbicides. After establishment, weeding can be done mechanically, although in the tropics it is often done manually.

Peppers production in glasshouses and other protective structures is significant primarily in areas where crops cannot be matured outdoors. Indeterminate cultivars developed for greenhouse production are carefully trained vertically on strings and pruned to efficiently use greenhouse space. The Dutch greenhouse system uses fertigated rockwool media similar to the system used for greenhouse tomato production. Night temperatures should be maintained at <15°C for best fruit development. Bees or mechanical agitation are used to improve greenhouse pollination. A bumble bee hive containing approximately 60 bees per 1440 m² provides sufficient greenhouse pollination. Manual pollination by workers is generally less efficient and considerably more expensive.

Principal sources: Elzebroek and Wind (2008); Janick and Paull (2008); George (2011); Bosland and Votava (2012); Russo (2012); Welbaum (2015)

The majority of peppers in the world, destined for fresh market, are harvested by hand. The reason for hand harvesting is quality. Hand-picked peppers are of a higher quality because humans can instantaneously reject mouldy, underripe, overripe or damaged pods. There is no abscission zone, so the pedicle of fruits must be carefully cut or expertly snapped by hand without damaging the brittle branches and surrounding leaves. Humans also do not pick as many leaves and stems as machines and there is an increased yield per unit area. The increased yield is associated with less damage to the plants as human pickers move through the field. Machine harvesters cause more damage and machine harvested plants take longer to recover and set more fruit. Mechanical harvesting is more common for processing crops because fruit damage is less critical if no storage is needed before processing. Peppers for processing are destructively harvested either by hand or machine. For small scale production of chilli powder, paprika, and other dried pepper products, entire plants with fully coloured fruit are cut and field dried when environmental conditions are favourable.

Picking the fruits may start 3-4 months after planting. The harvest time depends on the desired product: fruits are sometimes picked when they are unripe and green, and others are picked ripe, when the fruits are red, yellow, orange or brown. The harvesting of peppers is flexible and based on colour, fruit size, and/or wall thickness. Generally, the surface of older fruit is firmer, shinier, and waxier than younger fruit. More mature fruit tend to resist shrinkage after harvest, more than less-mature fruit whose cuticle is not fully developed. Green fruit are harvested after reaching their mature size, but before physiological maturity and colour change occur. Fruit are physiologically mature when the seed they contain are fully developed and they obtain their mature colour, which is often red or yellow. Some growers use accumulated heat units for scheduling harvests.

For large-scale production, mechanical harvest of the red chilli and paprika crops has been widely adopted in recent years, with more than 80% of the commercial crop in the USA harvested by machine. There are several different types of mechanical harvesters currently used for red chilli and paprika. The three most common picking heads are the finger-type, the belt-type, and the double helix. The finger-type head is designed with a series of counter- rotating bars with fingers. The fingers comb the plants to strip off the pods on to conveyor belts. The mechanism is aggressive and may harvest unwanted plant debris. A belt-type harvester has two sets of counter-rotating vertical belts imbedded with fingers that comb both sides of a plant. The most widely used picking head is the double-helix design. The helices may be vertical or oriented at an angle. The helices rotate in opposite directions to each other, snapping pods off of the plants and flipping them on to conveyor belts on either side.

Under greenhouse production, well-grown and managed crops of Capsicum on average can produce yields of approximately 15 kg/m². There is no information, however, available on yields of field grown C. baccatum. However, FAOSTAT (2016) reported yields of green chillies and peppers for South American countries where is it is the most widely grown Capsicum spp., may give an indication of its yield. In 2013, average yields were highest in Chile (60.98 t/ha), followed by Peru (9.28 t/ha), Ecuador (3.17 t/ha) and Bolivia (2.82 t/ha).

Principal sources: Elzebroek and Wind (2008); Janick and Paull (2008); Welbaum (2015)

Fresh market Fruits are susceptible to mechanical injury and may be easily damaged during shipment. After harvest, fruit for fresh market should be rapidly cooled to about 10°C to remove field heat. Peppers are washed in ambient or warm chlorinated (300 ppm) water to reduce postharvest diseases before storage or shipment.

Dried Peppers harvested for drying are dried using sun drying in the field or larger, commercial operations employ either tunnel or belt dryers. Both systems are more reliable and sanitary than sun drying. However, these methods use more energy, especially early in the harvest season when succulent pods are harvested and must be dried. Another drawback to tunnel and belt dryers is their limited capacity. The dehydrated pepper fruit is ground and rehydrated to 8-11% moisture, an optimal level for storage. Antioxidants such as ethoxyquin are sometimes added to reduce colour loss. Cold storage at 3°C is recommended.

Canning The most common pod types to be canned are New Mexican, pimiento and jalapeno. Pepper fruit are normally processed at 100°C, but long exposure time to this thermal treatment or to pressure processing can excessively soften the fruit. Acidification of the product reduces the pH below 4.6, decreases the thermal resistance of microorganisms, allows the canner to reduce the thermal exposure time and process peppers at atmospheric pressures. The pH of peppers has been shown to vary among early to late season harvests, along with the degree of ripeness. Therefore, concentrations of acidulent must be adjusted to account for the pH variability of the raw fruit. Properly canned fruit generally have a maximum shelf life of 2 years. In addition to pH considerations, fruit texture is a major concern of processors. Fruit softening of canned peppers can be minimized with calcium treatments. Calcium chloride is the preferred calcium source for both pimientos and jalapenos, although calcium lactate is also acceptable. In canned pimientos, the combination of citric acid and 0.02% calcium chloride to the product significantly increased both firmness and drained weight when compared to either treatment alone. The firmness of canned jalapenos is increased, without imparting bitterness, when 0.2% calcium chloride is added to the product.

Brining Pepper fruit that are usually brined include cherry, wax, pepperoncini, jalapeno and serrano. The pickling or brining process involves adding sufficient amounts of salt and acetic acid to prevent microbial spoilage; peppers packed in this manner have superior textural qualities as compared to canned peppers. The effectiveness of brining for preservation is related to the rate of acid diffusion into all parts of the fruit and the time required to reach an equilibrium pH of 4.6 or below. The primary areas for acid penetration are through the stems and calyxes and into the placentas. The interior of fruit walls is the last area to become acidified, and the entire process can take a minimum of 6 days. Blanching can also improve the rate of acid penetration into the fruit and therefore reduce the pH variability among fruit parts.

In most commercial operations, peppers are brined in a two-step process. First, fresh pepper fruit are placed in a primary brine to firm and preserve the fruit. After a minimum period of 2-8 weeks, depending on cultivar and process, the fruit are removed from the first brine, washed, graded a second time and then re-packed in finishing brine. Only the best quality fruit are packed whole or sliced in the finishing brine. Vinegar and salt levels may be reduced in the finishing brine and spices may be added for flavouring. This second brine is usually added to the fruit in the final container, and the container is sealed and hot-packed. A large portion of fruit are never packed in the second brine, instead they are chopped and blended into other food products after the initial brining.

Preservatives are often used in the initial brine to further prevent fruit softening and discoloration. Sodium bisulfite (0.5-1% by weight) is the most common preservative in pickled pepper. Sodium bisulfite is an effective preservative, but it imparts an off-flavour that is leached in the second packing brine. Bisulfite has also been implicated in certain food allergies experienced by asthmatics. Calcium chloride (0.25-0.50% by weight) can replace bisulfites, but is less effective at firming the pods, can impart bitterness at high concentrations, darken fruit colour and requires additional salt for optimal rigidity of the fruit. Brined pepper fruit can be produced without preservatives by using a more costly refrigerated process. Cold temperatures allow the fruit to imbibe brine completely, while slowing the growth of bacteria that can soften the fruit. The first 4-8 weeks are the most critical period of the brining operation. If the conditions are not optimal, the fruit can soften. After 6-8 weeks in cold storage, the fruit reach an osmotic equilibrium with the brine solution and further softening does not occur. Brined fruit without chemical preservatives are then packed in finishing brines with higher vinegar and salt concentrations than those with bisulfite.

Fresh chilli peppers are not as chilling sensitive as bell peppers. Chilli peppers stored above 7.5°C suffer more water loss, shrivel, colour change, and decay. Storage at 7.5°C is considered the best for maximum shelf-life of 3-5 weeks. Chillies can be stored at 5°C for at least 2 weeks without visible signs of injury. Storage at this temperature reduces water loss and shrivelling, but after 2-3 weeks, chilling injury is mostly detected as discolouration of the seeds. Ripe or coloured chillies are less chilling sensitive than mature green chillies. Unlike tomatoes, peppers are not climacteric. Many chilli peppers do not ripen after harvest when treated with ethylene. Bell pepper ethylene production rates are very low in the range of 0.1-0.2 ml/kg/h at 10-20°C. However, some chillies, such as habaneros, show increased ethylene production during ripening and may produce over 1 ml/kg/h at 20-25°C. Responses to added ethylene depend on the particular type of chilli. Chilli ‘Poblanos’ for example may respond to ethylene treatment, while ‘Jalapeno’ peppers do not. As with bell peppers, holding partially coloured chilli peppers at warmer temperatures of 20-25°C with high humidity (>95%) is effective to complete colour development. Adding ethylene may further enhance ripening but the response is cultivar dependent. Red and yellow physiologically mature bell peppers are more expensive to produce than green because fruits must remain on the plant longer to develop their mature colour. This reduces total yields because mature peppers inhibit the set and growth of new fruit. Fruit are also susceptible to disease and insect attack during their extra time on the plant. Mature red fruit also have 10 times more provitamin A content, softer texture, and higher soluble sugar content, which also adds to their value. The red colour develops because of increased carotenoid synthesis and a breakdown of chlorophyll. As green bell peppers begin to turn to red, their colour first changes to brown during the transition because both the red carotenoids and green chlorophyll are in the fruit wall simultaneously. This is often called the “chocolate” stage. Once harvested, chocolate peppers will remain brown because they do not easily ripen after harvest. In some markets, chocolate peppers have less value because the colour is unappealing to consumers. High relative humidity is necessary to limit desiccation. Water-soluble wax is sometimes used to coat peppers to decrease shrivelling and increase storage life. However, waxing may increase the possible incidence of bacterial soft rot. Bell peppers are also wrapped with a thin layer of plastic film individually or grouped in a plastic tray to preserve freshness and reduce mechanical damage from handling. Waxed or film-wrapped peppers can be stored from 10-14 days at 13°C. Shelf life varies among cultivars. Deterioration is often due to moisture loss and some fruit types are more prone to desiccation than others. Peppers generally do not respond well to controlled atmosphere storage. Low O₂ atmospheres (2-5% O₂) alone have little effect on quality and high CO₂ atmospheres (>5%) can cause pitting, discoloration, and softening, especially at temperatures >10°C. Atmospheres of 3% O₂ + 5% CO₂ are more beneficial for red than green peppers stored at 5-10°C.

Principal sources: Janick and Paull (2008); Welbaum (2015)

Sporophytic chromosome count for the species is 24 (IPCN Chromosome Reports, 2014). C. baccatum has a longer karyotype length (and increased DNA content), 3-4 chromosomes with active nucleolus organizer regions, increased GC-enriched heterochromatin (7-9%), and a highly complex heterochromatin banding pattern compared to other Capsicum species (Moscone et al., 2007). A list of known genes can be very useful to pepper breeders, especially if a collection of germplasm that contains representative specimens is available. In 1965, Lippert and colleagues produced a gene list for pepper (Lippert et al., 1965) which included 50 genes and a standardization of rules for naming and symbolizing. Wang and Bosland (2006) provided the most recent update, adding 92 previously unreported genes to bring the total to 292.

The US National Plant Germplasm System houses an extensive Capsicum germplasm collection at the Southern Plant Introduction Station located in Griffin, Georgia. This gene bank has a worldwide collection of approximately 5000 Capsicum accessions. Globally, there are several other gene bank collections. Many of the accessions in each collection are duplicates of material maintained in other collections. The most active collections are the Asian Vegetable Research and Development Center (AVRDC) in Tainan, Taiwan, the Centro Agronomico Tropical de Investigations y Ensenanza (CATIE) in Turrialba, Costa Rica, the Centre for Genetic Resources (CGN) in Wageningen, the Netherlands, and the Central Institute for Genetics and Germplasm in Gatersleben, Germany. There are important South American collections of C. baccatum holding wild and domesticated forms. The collection of the Instituto Nacional de Innovación Agraria (INIA), Peru, holds 712 Capsicum accessions of which 70 are domesticated C. baccatum. The collection of the Centro de Investigaciones Fitoecogenéticas de Pairumani (CIFP) in Bolivia holds 487 Capsicum accessions of which 217 accessions are of domesticated C. baccatum and 11 are of the wild species C. baccatum var. baccatum. This latter collection conserves an important amount of C. baccatum genetic diversity compared to international Capsicum collections as Bolivia is a primary centre of diversity of cultivated C. baccatum var. pendulum (Zonneveld et al., 2015). Embrapa Clima Temperado, a research institution in southern Brazil, maintains a collection of 347 Capsicum accessions, including 286 of C. baccatum (Barbieri et al., 2007).

Throughout Latin America, it is not uncommon to find wild and semi-wild Capsicum species growing in close proximity to cultivated species, in domestic gardens or at the edges of cultivated fields. This situation allows introgressive hybridization to takes place between the domesticated species and closely related wild species or sub-species, spontaneously giving rise to novel or intermediate forms which are then selected and propagated by observant farmers in an ongoing process of on-farm crop evolution (Zonneveld et al., 2015).

These focus on fruit attributes including yield, colour, size, shape, and pungency, and fruit and foliar disease resistance in open field and protected culture. Varying levels of resistance to powdery mildew caused by Leveillula taurica have been reported in C. baccatum var. microcarpum and C. baccatum var. pendulum. C. baccatum is also a valuable species in Capsicum breeding, in particular as a source of disease resistance against anthracnose and powdery mildew.

Capsicum breeders are faced with the arduous task of assembling into a cultivar the superior genetic elements necessary for increased yield, protection against production hazards and improved quality. Each type has its own unique set of characteristics that must be met in order to be commercially acceptable. Breeders are therefore faced with a plethora of unique objectives, and in order to achieve those objectives, they may use quite a few different breeding methods. The methods used are determined by the breeder to best fit the goals of the breeding programme.

The first pepper breeders, the indigenous people of tropical America, used mass selection to domesticate the five different species of Capsicum. Another breeding method used by many pepper breeders is the pedigree method, which involves keeping records of the matings and their progeny. A good cultivar can be made better by using the backcross method, which uses a successful cultivar as a recurrent parent following an initial cross between that successful cultivar and a separate individual that serves as a donor parent for a given desired character. Following successive backcrosses to the recurrent parent, the breeder arrives at a cultivar identical to the recurrent parent, but containing the additional desired trait from the donor parent. Several other breeding methods have been successful. For example, recurrent selection, where individual plants are selected from a population followed by intercrossing to form a new population. Mutation breeding is a means by which mutations are generated in peppers to improve economically important traits or to eliminate deleterious traits. It is not a major breeding method, but may be a means of producing novel mutants of interest.

Biotechnology is being used to develop new cultivars. For many years, Capsicum spp. were recalcitrant to the methods of genetic transformation. Reports that pepper has been successfully transformed using Agrobacterium tumefaciens has given impetus for commercial seed companies to begin programmes introducing novel genes into peppers. Since the late 1980s, efforts to tag and map identified genes using molecular methods have provided markers linked with important traits for use in marker-assisted breeding programmes for sweet and hot pepper. Utilizing mapping populations developed from a series of interspecific crosses, RFLP, AFLP, RAPD, and SSR markers have been integrated to improve the average marker density and facilitate identification of simply inherited and complex attributes.