Resistance in groundnut (Arachis hypogaea L.) to Aphis craccivora (Koch)

The behaviour, development and reproductive capacity of Aphis craccivora, vector of a number of groundnut viruses, are compared on a range of susceptible and resistant genotypes. Field trials demonstrated no significant difference between genotypes in the rate of arrival of alates, but population development was slower, and subsequent population decline faster, on the genotype EC 36892 (ICG 5240). Behavioural studies in the screenhouse, likewise showed no inhibition to alighting onto EC 36892 though choice tests demonstrated a significant redistribution of the population in favour of the susceptible genotype TMV 2 (ICG 221) over the following 10 h. In clip cage experiments, development was faster and nymphal numbers were higher on the genotype TMV 2 compared to EC 3689

Screening Groundnut Breeding Lines for Resistance to Aphids, Aphis craccivora Koch

Some 37 F6 breeding populations were compared with 4 control varieties in a screenhouse study to combine rosette virus [groundnut rosette umbravirus] resistance with resistance to the vector Aphis craccivora. Following artificial infestation, mean aphid populations were recorded 10 and 15 days after infestation. The genotype ICG 12991 had the lowest rate of nymph development, low fecundity and smaller aphids compared with the controls

Mechanisms of resistance to groundnut rosette

Rosette (caused by rosette assistor virus, groundnut rosette virus and satellite RNA) resistance in 3 groundnut genotypes (ICGV-SM 90704, ICG 12991 and JL 24) was evaluated, using a vector or mechanical transmission of the virus complex. Branches from rosette-infected plants (groundnut cv. Malimba) were grafted onto 23-day-old healthy stocks of the 3 genotypes, grown in pots in a greenhouse. Eighteen days after grafting, all the new shoots of ICG 12991 and JL 24 stocks showed severe rosette symptoms. The differences in rosette incidence recorded from the graft transmission and field observations may involve resistance to Aphis craccivora. Thus, an experiment was carried out to assess the vector performance on the 3 genotypes. Thirty days after sowing the 3 genotypes in pots in a greenhouse, young leaves were exposed to 5 viruliferous A. craccivora alatae (winged). Aphids were counted 10 days after infestation (DAI) on each plant. Exposed plants were left in a greenhouse up to 60 days after infestation to record rosette symptoms. Results indicated highly significant differences in aphid population counts between the 3 genotypes. At 10 DAI, increased numbers of aphids (alatae plus nymphs) were observed on ICGV-SM 90704 and JL 24, with an average of 93 and 96 aphids per plant, respectively. In contrast, aphid number on ICG 12991 fell from 5 to 3 per plant. There were also significant differences in disease expression at 60 DAI, since JL 24 showed 100% disease incidence, while no symptoms were noted on ICG 12991. Only mild symptoms were observed on ICGV-SM 90704

Technological options that respond to demands and market opportunities with focus on crops and livestock

Technology development is a core area of agricultural research, and the increasing global focus on client-demand and market oppourtunities is intended to increase its releance and effectiveness. This theme focuses on the achievements of and lessons learnt from technological optipns developed for crop and livestock systems including breeding, management practices and processing and appropriate technolgies, knowledge, information and methods that enhance productivity, value addition and the competitiveness of the products in both national and international markets. A number of research providers as well as public sector bodies such as national agricultural systems and universities, non-governmental organisations which have links to broad farmer networks have become increasingly involved in research activities. Consequently, agricultural researchers have and are continually developing a broad range of technological options to secure the production of safe food and non food cash crops and to achieve the most efficient and ecologically sound use of natural resources; soil, water and energy. It is however apparent that farmers prefer packages of information not just pest management strategies alone but a total package including other aspects such as soil and weed management options

Spatiotemporal Separation of Groundnut Rosette Disease Agents

Analysis by triple-antibody sandwich enzyme-linked immunosorbent assay of groundnut samples from fields in two seasons from different regions of Malawi showed the absence of groundnut rosette assistor virus (GRAV) from some plants showing groundnut rosette disease symptoms and the presence of GRAV in some symptomless plants. Viruliferous Aphis craccivora collected from fields transmitted either GRAV alone, groundnut rosette virus (GRV) with its satellite RNA (sat RNA), or all three agents together, in different proportions. More plants became infected with all three agents when increasing numbers of potentially viruliferous aphids were used per plant, suggesting a dosage response. Electrical penetration graph studies of aphid stylet activities indicated successful transmission of GRV and its sat RNA during both the "stylet pathway phase" and salivation into sieve elements, whereas GRAV was transmitted only during the latter phase. Aphids transmitted all three agents together only during the salivation phase. Reverse-transcriptase polymerase chain reaction testing of viruliferous aphids and of inoculated plants revealed no correlation between the presence of all three agents in prospective aphid vectors and their simultaneous transmission to groundnut plants. These results show that separation of the groundnut rosette disease agents occurs over time and space

Condensed tannin levels and resistance of groundnuts (Arachis hypogaea) against Aphis craccivora

A strong negative relationship was found between the concentrations of procyanidin, a condensed tannin, in the leaf bud petioles of seven genotypes of groundnut (Arachis hypogaea) and fecundity of the aphid Aphis craccivora on the same genotypes. Genotype EC 36892 contained the highest amount of procyanidin per weight of fresh petiole (ca 0.7%) and aphids feeding on this genotype produced significantly fewer offspring than aphids reared on genotypes with low procyanidin levels. It is proposed that testing for high procyanidin concentrations may provide plant breeders with a quick and relatively simple method to screen new groundnut genotypes for resistance against Aphis craccivor

Groundnut rossette: A virus disease affecting groundnut production in Sub-Saharan Africa

Groundnut (peanut, Arachis hypogaea L.) is cultivated in the semiarid tropical and subtropical regions of nearly 100 countries on six continents between 40°N and 40°S (Fig. 1). For people in many developing countries, groundnuts are the principal source of digestible protein (25 to 34%), cooking oil (44 to 56%), and vitamins like thiamine, riboflavin, and niacin (65)..

Identification and mapping of AFLP markers linked to peanut (Arachis hypogaea L.) resistance to the aphid vector of groundnut rosette disease

Groundnut rosette disease is the most destructive viral disease of peanut in Africa and can cause serious yield losses under favourable conditions. The development of disease-resistant cultivars is the most effective control strategy. Resistance to the aphid vector, Aphis craccivora, was identified in the breeding line ICG 12991 and is controlled by a single recessive gene. Bulked segregant analysis (BSA) and amplified fragment length polymorphism (AFLP) analysis were employed to identify DNA markers linked to aphid resistance and for the development of a partial genetic linkage map. A F2:3 population was developed from a cross using the aphid-resistant parent ICG 12991. Genotyping was carried out in the F2 generation and phenotyping in the F3 generation. Results were used to assign individual F2 lines as homozygous-resistant, homozygous-susceptible or segregating. A total of 308 AFLP (20 EcoRI+3/MseI+3, 144 MluI+3/MseI+3 and 144 PstI+3/MseI+3) primer combinations were used to identify markers associated with aphid resistance in the F2:3 population. Twenty putative markers were identified, of which 12 mapped to five linkage groups covering a map distance of 139.4 cM. A single recessive gene was mapped on linkage group 1, 3.9 cM from a marker originating from the susceptible parent, that explained 76.1% of the phenotypic variation for aphid resistance. This study represents the first report on the identification of molecular markers closely linked to aphid resistance to groundnut rosette disease and the construction of the first partial genetic linkage map for cultivated peanu

Registration of ICG 12991 peanut germplasm line

ICG 12991 is a short duration (90–110 d to maturation), drought-tolerant, spanish-type peanut (Arachis hypogaea L. subsp. fastigiata Waldron var. vulgaris Harz.) germplasm line (Reg. no. GP-122, PI 639691) with a high level of field resistance to groundnut rosette disease (Naidu et al., 1999a; Subrahmanyam et al., 2000). Groundnut rosette disease results from a synergism of three agents: Groundnut rosette assistor virus (GRAV, a luteovirus), Groundnut rosette virus (GRV, an umbravirus), and a satellite RNA (sat RNA) of GRV. ICG 12991 was originally collected from a farmer’s field in south India in 1988. In 1994, ICRISAT introduced ICG 12991 into Malawi for evaluation during a germplasm screening program for resistance to groundnut rosette disease and early leaf spot disease (caused by Cercospora arachidicola S. Hori). Subsequently, ICG 12991 was released in Malawi as ‘Baka’ in 2001 and in Uganda as ‘Serenut 4T’ in 2002, following extensive testing and distribution by the national programs of each country. Resistance to groundnut rosette disease in ICG 12991 is due to aphid resistance, not due to resistance to the virus complex (Naidu et al., 1999b)