Zeatin-induced shoot regeneration from immature chickpea (Cicer arietinum L.) cotyledons

For the purpose of developing an in vitro regeneration system for chickpea (Cicer arietinum L.), an important food legume, immature cotyledons approximately 5 mm long were excised from developing embryos and cultured on B5 basal medium supplemented with 1.5% sucrose and various growth regulator combinations. Only non-morphogenic callus was formed in response to concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D), naphthaleneacetic acid (NAA) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) previously reported to induce somatic embryogenesis on immature soybean cotyledons. However, 4.6, 13.7, and 45.6 M zeatin induced formation of white, cotyledon-like structures (CLS) at the proximal end of immature cotyledons placed with adaxial surface facing the agar medium. No morphogenesis, or occasional formation of fused, deformed CLS, was observed when zeatin was replaced with kinetin or 6-benzyladenine, respectively. The highest response frequency, 64% of explants forming CLS, was induced by 13.7 M zeatin plus 0.2 M indole-acetic acid (IAA). Within 20–40 days culture on zeatin, shoots formed at the base of CLS on approximately 50% of CLS-bearing explants, and proliferated upon subsequent transfer to basal medium with 4.4 M BA or 4.6 M kinetin. This regeneration system may be useful for genetic transformation of chickpea.     

Effects of supplemental nitrate and thermal regime on the nitrogen nutrition of chickpea (Cicer arietinum L.)

Summary Nodulated chickpea plants were grown in pots in a glasshouse programmed to simulate either hot (32.5°C day/18°C night) or warm (25°/18°C) thermal regimes characteristic of those experienced by crops grown in different seasons or locations in the semi-arid tropics. The plants were irrigated with nutrient solution either devoid of inorganic nitrogen or containing 0.71, 1.43 or 2.86 mM nitrate. Increasing concentrations of supplemental nitrate stimulated the rate of dry matter production by vegetative plants in both thermal regimes. Differences between vegetative dry weight of plants given nitrate and those relying exclusively on symbiotic dinitrogen fixation were greatest in the hot regime where the durations of vegetative growth were shorter. However, symbiotically-dependent plants and those given 0.71 mM nitrate continued to produce branches throughout the reproductive period, particularly in the warm regime. As they matured, these plants became more comparable in vegetative stature to those which had received greater concentrations of nitrate and had established final branch numbers earlier (i.e prior to main pod-fill). Potential seed yields were determined primarily by the number of potential reproductive sites (nodes) available (i.e. by the extent of branching) which largely determined the number of seeds harvested. Since final branch numbers in all nitrate treatments were greatest in the warm regime, yields were also larger than those at 32.5°C. The implications of these data for the nitrogen economy of chickpea crops is discussed.One of a series of papers resulting from a collaborative project with the International Crops Research Institute for the Semi-Arid Tropics, India; sponsored by the UK Overseas Development Administration.     

Genotype-Dependent morphogenetic potentiality of various explants of a food legume,the pigeon pea (Cajanus cajan L.)

Summary The morphogenetic response of various explants of seven different cultivars of a food legume, the pigeon pea (Cajanus cajan L.), has been studied. The stimulation and elongation of shoot buds into shoots derived from the mature embryo axis and intact seed on Murashige and Skoog’s medium supplemented with 2.32µM kinetin and 22.2µM benzyladenine was found to be optimum in Murashige and Skoog’s medium supplemented with 0.46µM kinetin, 0.53µM naphthalene acetic acid, and 0.29µM gibberellic acid. Even though the response of these two explants for formation of shoot buds in all the genotypes is 30–100% depending on media composition, subsequent growth and elongation of these shoot buds into plants is genotype dependent and is restricted to two genotypes. Cotyledon and epicotyl explants of pigeon pea cultivars on the other hand differentiated directly into four to eight and two to four shoots, respectively, depending on the media composition and genotype. In vitro rhizogenesis of regenerated shoots was 80% and the survival of these plantlets in the field was 70–80%. NCL Communication no.: 5667.     

Somatic embryogenesis from chickpea (Cicer arietinum L.) inmature cotyledons: The effect of zeatin, gibberellic acid and indole-3-butyric acid

Studies were conduced to test the effects of various cytokinins on somatic embryogenesis from chickpea (Cicer arietinum L.) immature cotyledons. Zeatin (13.7 μmol) added, to B5 basal medium, supplemented with 1.5 % sucrose and 0.2 μmol indole-3-acetic acid, was the most effective cytokinin. Lobular structures obtained from cotyledons cultures were transferred to B5 basal medium supplemented with gibberellic acid and indole-3-butyric acid at different concentrations. The most effective treatment was B5 medium containing 14.4 μmol gibberellic acid plus 1.0 μmol indole-3-butyric acid in which 42.8 % of lobular structures cultured formed normal somatic embryos. High conversion of embryos into plantlets (61.0–65.2 % embryos regenerated plants) was observed when germinated embryos were placed on plant development medium.     

Nodulation,nitrogen fixation and nitrogen uptake in pigeonpea (Cajanus cajan (L.) Millsp) of different maturity groups

Summary The seasonal patterns of nodulation, acetylene reduction, nitrogen uptake and nitrogen fixation were studies for 11 pigeonpea cultivars belonging to different maturity groups grown on an Alfisol at ICRISAT Center, Patancheru, India. In all cultivars the nodule number and mass increased to a maximum around 60–80 days after sowing and then declined. The nodule number and mass of medium- and late-maturing cultivars was greater than that of early-maturing cultivars. The nitrogenase activity per plant increased to 60 days after sowing and declined thereafter, with little activity at 100 days when the crop was flowering. At later stages of plant growth nodules formed down to 90 cm below the soil surface but those at greater depth appeared less active than those near the surface. All the 11 cultivars continued to accumulate dry matter until 140 days, with most biomass production by the late-maturing cultivars (up to 11 t ha⁻¹) and least by the early-maturing determinate cultivars (4 t ha⁻¹). Total nitrogen uptake ranged from 69 to 134 kg ha⁻¹. Nitrogen fixation by pigeonpea was estimated as the difference in total nitrogen uptake between pigeonpea and sorghum and could amount to 69 kg N ha⁻¹ per season, or half the total nitrogen uptake. Fixation by pigeonpea increased with crop duration, but there were differences within each maturity group. The limitations of the methods used for estimating N₂ fixation by pigeonpea are discussed. Submitted as J.A. No. 552 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).