Inga edulis

Symbiosis

The Inga plant can also form symbiotic relationships where nitrogen gas can be fixated by rhizobial bacteria and mycorrhiza as other legumes can. Surveys have shown that Inga edulis undergo a mutualistic relationships with the bacterial strain of Bradyrhizobium.^[8]

• 
  Flowers
• 
  Mature and young pods

Synonyms

This plant has a convoluted history of synonymy with Inga vera. The plants discussed under that name by Brenan and Kunth are actually I. edulis, whereas that based on the writings of Carl Ludwig Willdenow refers to the actual I. vera. Inga edulis in works referring back to authorities other than von Martius usually refers to Inga feuilleei.^[9]

Synonyms of Inga edulis Mart.:

• Feuilleea edulis (Mart.) Kuntze^[9]
• Inga benthamiana Meisn.^[9]
• Inga edulis
  var. grenadensis Urb.^[10]
• Inga minutula (Schery) T.S.Elias[10]
• Inga scabriuscula Benth.^[9]
• Inga vera Kunth^[9]
• Inga vera sensu Brenan^[9]
• Inga ynga (Vell.) J.W.Moore^[9]
• Mimosa inga L.^[10]
• Mimosa ynga Vell.^[11]

Ecology

The natural distribution of Inga edulis spreads from Central to South America and ranges from subtropical dry to tropical wet conditions.^[12] It can be found at elevations from sea level up to 2200 m. Inga edulis grows best when mean annual daytime temperature ranges from 23 to 30 °C. However, it can tolerate 18–35 °C. During the resting period mature trees can survive −2 °C while young plants are killed at 0 °C. Preferred annual precipitation ranges from 1200 to 2500 mm but 640 to 4000 mm of annual precipitation can be tolerated also. Inga edulis can be grown on a widely varying range of soil conditions. It prefers a soil pH of 5–6.5 but can also grow in very strongly acidic soil down to a pH of 4.5 or moderately alkaline conditions up to pH 8.^[13] The natural habitat of Inga edulis includes margins of large rivers like the Amazon, thickets below high water line and wooded swamps.^[12] Therefore, the tree tolerates temporarily waterlogged soils for 2–3 months each year. However, it can also tolerate drought seasons up to 6 months.^[14] Further Inga edulis can cope with heavy soils or slope fairly well.^[12] In terms of soil fertility, Inga edulis is not only unpretentious but has the potential to improve soil quality. As a leguminous tree, Inga edulis can compensate for nutrient depleted soils by fixing nitrogen with its root nodules. Ammonium and nitrates found in soil typically result in nodulation reduction. Inga edulis is an exception, as its nodules increase in size when ammonium levels are at 5 mM. Nitrate on the other hand did not benefit Inga edulis and continued to show properties that prevented nodulation. Additionally to nitrogen, Inga edulis is reported to significantly increase the extractable Phosphorus content in the soil and thus further ameliorates degraded soils.^[15]

Cultivation

Inga edulis is widely cultivated in agroforestry systems in its neotropical dispersal area. This form of cultivation, often associated with coffee or cocoa culture, is widely known since pre-Columbian times.^[16] Germination of Inga edulis seeds is fairly easy as the seeds are recalcitrant and often germinate already in the pod. However, seeds lose their ability to germinate after two weeks of storage.^[14] Direct sowing of the seeds is possible, but the establishment of seedlings with already a certain height can decrease competition with noxious weeds and thus increase growth.^[17] Further, the inoculation with rhizobia and mycorrhizal fungi in depleted soils is recommended to promote growth.^[18] These inoculi can easily be produced by collecting soil, nodules and fine roots from mature, nodulated inga edulis stands.^[12] Inga edulis seems to be very resistant to pests and diseases. Minor damages can result of fungal attacks in the seedling stage. Mature Inga edulis can be defoliated by Lepidoptera larvae. Also, fruit fly larvae often damage the seed testa. In Ecuador, Inga edulis in specially susceptible to mistletoe infestations.^[14]

Uses

Food crop

Inga edulis has been cultivated as a fruit tree for millennia and is widely sold on the local South American marketplace, mainly for the sweet, succulent pulp surrounding the seeds. The white pulp (aril) is consumed raw as a sweet snack, though it is less nutritious than the seeds. Toxic compounds such as trypsin and chymotrypsin inhibitors contained in the seeds of Inga edulis are destroyed through cooking.^[6]