Groundnut

Morphology And Growth

• The leaves of the cultivated Groundnut are paripinnate with two piece of opposite, sub-sessile, obovate leaflets with entire cilliate margin.
• They are born spiralsin a 2/5th phyllotaxy.
• The leaves are arranged on the main axis and higher order branches in a distichous fashion.
• Stipules are prominent, linear and adnate, becomes free of petiole at the pulvinus.
• The leaflets are borne on a slender, grooved and jointed rachis.
• The leaves exhibit nyctiotropic movements.
• Groundnut cultivars differ in their leaf colour, shape and hairiness and size.
• The stomata present on both sides of leaf.

• With aging, stems with hallow cylindrical and shed hairs. In annual species, twigs do not turn woody.
• The main axis develops from the terminal epicotyl bud and is flancked by two opposite cotyledonary laterals (n+1).
• The stem thickness is also a variable character, " bunch" types generally have thicker stems than "spreading "varieties.
• The internodes are short, highly condenced at the base but are large at the higher nodes.

• The advantitious roots commonly form from the aerial branches that come in contact with soil.
• A well developed tap root may penetrate to a depth of 130 cm but rarely goes beyond 90 cm.
• The root system is normally concentrated between a depth of 5 and 35 cm.
• The spreading confined to a radious of 12 to 14 cm.
• The spreading types have a more vigorous root system than the bunch types.

• Solitary or in raceme, very irregular (Papilionaceous).

• After pollination, meristematic region grows at the base of the ovary and become a stalk like structure (gynophore) referred to as Peg Which bend downward and forces the ovary into the soil.
• The peg carrying the ovary pushes itself into the soil.

• Flowering in groundnut begins 20 to 30 days after emergence, depending on genotype and environment, especially temperature.
• The number of days required for the commencement of flowering is reduced from 38 to 25 days in sub sp, hypogaea as the daily mean temperature rises from 200 to 300C.
• Depending upon the cultivar, duration and season, the most prolific period of flowering takes place between 5 and 11 weeks, with a high degree of first-formed flowers producing mature fruits.
• The soil moisture status during the growth period of crop influences flowering most significantly.
• About 4 or 5 stages of flowering have been recognized. Few flowers are produced during the first stage, followed by a stage of rapid flowering.
• A peak is reached at the third stage, followed by a decline. A few of late-opening flowers produce mature fruits.
• The groundnut plants produce more flowers than they can sustain to develop pods and seeds.
• About tow-fifths of the flowers normally fail to develop from the outset, while another two-fifths produce only pegs and only one out of seven produces mature fruit.
• Both the pattern and peak of flowering depend greatly on the cultivar and environment.
• Normally only one flower in an inflorescence reaches anthesis on a given day in var vulgaris, two or more flowers may reach anthesis on the same day.
• During anthesis the hypanthium elongates slowly and buds increase in length from about 6-10 mm to 10-20 mm and to about 50-70 mm at the time of anthesis.
• Cold and wet weather conditions may delay bud opening, which normally occurs at the beginning of the light period.
• The anthers may dehisie 7-8 hours before flowers open and stigma becomes receptive from 24 hours before to 12 hours after the flower opening.

• The stigma normally protrudes above the anthers and is receptive before anthesis. Since the stigma is enclosed in the keel. self-pollination is the rule.
• In some cases the stigma and anthers are exserted from the keel leading to cross-pollination.
• About 1.0 to 3.9% cross-pollination has been reported to take place naturally. Several bee species have been found to be the pollinators in out-crossing of groundnuts.
• Fertilization is completed within 6 hours of pollination. flowers withering simultaneously (5 to 6 hours).

• After fertilization flower droops, corolla closes. the calyx tube bends and the flower withers.
• The ovary at the base of the calyx becomes mobile for growth during the early development of the embryo. requiring about a week's time. which may vary with cultivars and climate.
• An intercalary meristem below the ovary then gets activated.
• The green ovary turns purplish from the tip downwards.
• The developing ovary pierces through the floral parts by the activity of the meristem to reveal an elongating peg (carpophore) which is a stalk-like structure bearing the fertilized ovules at the tip.
• Its growth is positively geotropic until it penetrates the soil to some depth, the tip then becomes diageotropic.
• After this the ovary starts developing into a fruit. The pegs failing to contact and enter soil. after expanding to about 15, cm. usually wither away.
• The pegs may be either pigmented or green. though the portion of the peg in soil is white.
• The length of the penetrating pegs determines the depth at which groundnut pods are formed.
• The cultivar differences for peg length were found to be closely related to the differences in their branching pattern.
• The cultivars with sequential-branching pattern produce most of the flowers that produce mature pods at the basal nodes and hence have shorter pegs than the cultivars with alternate branching pattern.
• The peg-thickness varies from about 1 to 2 mm.

• Similar to the fact that all the pegs formed do not grow long enough to reach the soil and develop into pods. all the pegs that enter the soil also do not form mature pods.
• There are significant cultivar differences in the proportion of pegs developing into pods. The groundnut fruit. normally referred to as a pod about 10 cm long and indehiscent.
• The mature pod normally contains 2 to 4 seeds. occasionally even 5 or 6 seeds per pod also have been recorded.
• Single seeded pods are produced when all the ovules except the proximal one get aborted.
• The usual pod size is. about 2.7 x 6.0 cm. The fruit consists of two structurally dehiscent but functionally indehiscent valves .
• The pods splitting along the longitudinal suture only after pressing.
• The ovule grows before fertilization and continues to do so even after fertilization to some extent.
• The embryo which is dormant during peg elongation. begins to grow 3 to 4 days after the pod begins to develop.
• The basal ovule develops first and when the peg reaches its maximum depth. it turns dia-geotropic and almost horizontal.
• The pod starts developing only after the peg has ceased to elongate; the pods begin to enlarge from base at apex .
• The pod expands rapidly in the soil by the development of a large parenchymatous tissue (endocarp) lying between the ovules and shell layers. As the ovules begin to grow the endocarp recedes and disappearing totally when the seeds fully mature.
• The inner side of the shell turns increasingly dark brown owing to increased tannin content. finally becoming very dark brown on maturation. which takes about 60 days after fertilization.
• The size and shape of mature pods and seeds are governed by several intrinsic and external factors including cultivar, soil and cultural practices.
• Temperature extremes may prolong pod maturation. the optimum temperature during pod development being :31 to 33°C. Lower soil temperatures (around 23°C) have been found to increase the number of pods and pod weight, but pods develop over a Longer period of time.
• The tip of the indehiscent groundnut fruit ends in an appendage called the beak whose prominence varies greatly according to the genotype. This character has been widely used to classify groundnut cultivars.
• The pod constriction is an important character since it affects the seed development.
• The non-constricted pods generally have seeds with their ends flattened and remain in contact with other seeds in the pod which may result in embryo damage such seeds also tend to split easily during shelling.
• On the contrary pods with deep constrictions tend to carry soil on them and break during.harvesting and shelling; decreasing their market value.
• Most commercial varieties have constriction between each seed. Pod constriction shows considerable variation both Within and between cultivars, however the range of variation is not great enough to prevent Visual classification .
• Pod reticulation (venation. ribbing. ridging) on the shell is a prominent Visual characteristic exhibited differently by groundnut cultivars.
• Reticulation also contributes to the cleanliness of pods coming out of the soil at the time of harvesting. Five grades of reticulation have been recognized : smooth. slight, moderate. prominent and very prominent.
• Pod size which is influenced by genotype, soil and environmental factors, can also be used to distinguish groundnut cultivars.