Fusarium wilt (Fusarium udum Butler) is an important biotic constraint to pigeonpea (Cajanus cajan L.) production worldwide. Breeding for fusarium wilt resistance continues to be an integral part of genetic improvement of pigeonpea. Therefore, the study was aimed at identifying and validating resistant genotypes to fusarium wilt and determining the magnitude of genotype × environment (G × E) interactions through multi-environment and multi-year screening. A total of 976 genotypes including germplasm and breeding lines were screened against wilt using wilt sick plot at Patancheru, India. Ninety two genotypes resistant to wilt were tested for a further two years using wilt sick plot at Patancheru. A Pigeonpea Wilt Nursery (PWN) comprising of 29 genotypes was then established. PWN was evaluated at nine locations representing different agro-climatic zones of India for wilt resistance during two crop seasons 2007/08 and 2008/09. Genotypes (G), environment (E), and G × E interactions were examined by biplot which partitioned the main effect into G, E, and G × E interactions with significant levels (p ≤ 0.001) being obtained for wilt incidence. The genotype contributed 36.51% of resistance variation followed by the environment (29.32%). A GGE biplot integrated with a boxplot and multiple comparison tests enabled us to identify seven stable genotypes (ICPL 20109, ICPL 20096, ICPL 20115, ICPL 20116, ICPL 20102, ICPL 20106, and ICPL 20094) based on their performance across diverse environments. These genotypes have broad based resistance and can be exploited in pigeonpea breeding programs.

A survey was conducted in 2010-2011 rabi cropping season to obtain information on the distribution and incidence of chickpea diseases in respect to soil type, cultivar used, seed treatment in central and southern parts of India. Local cultivars predominated in most farmers' fields (25% -48%). 63% of the farmers were practices seed treatment with fungicide. Dry root rot and collar rot diseases were found at all of the sites and incidence ranged from 8.9% -10.3% and 7.1% -10.5% respectively irrespective of cultivar type and locations. Incidence of wilt and black root rot disease ranged from 9.7% -13.8% and 6.6% -7.4% respectively. Black root rot disease was found in Andhra Pradesh and Karnataka states only. The result indicated that dry root rot and collar rot is currently highly distributed in all surveyed chickpea growing areas of central and southern parts of India. Therefore, possible management options are vital to alleviate the problem.

Sterility mosaic disease (SMD) caused by Pigeonpea sterility mosaic virus and vectored by the eriophyid mite is a serious disease of pigeonpea in almost all pigeonpea-growing areas. Managing the disease with chemicals such as acaricides is very difficult, non-eco-friendly and costly; hence, host plant resistance is the best strategy implemented to manage this disease. In this context, 28 pigeonpea genotypes identified as resistant from preliminary screening of 976 pigeonpea accessions were evaluated in field at eight different agro-ecological locations in India for the stability of their resistance against SMD during 2007SMD during /2008SMD during and 2008SMD during /2009. Genotype plus genotype 9 environment (GGE) analysis partitioned main effects into genotype, environments and G 9 E interactions and showed significant effects (P \ 0.001) for SMD percentage incidence. Environment variance had the greatest effect (76.68 %), indicating the maximum variation in the disease due to the environment. At Bangalore, Dholi and Rahuri locations, all genotypes were susceptible to SMD with mean disease incidence of 71.1, 50.4 and 32.6 % respectively. However, most of the genotypes were resistant at four locations, Akola, Badnapur, Patancheru, and Vamban, and moderately resistant at Coimbatore. The GGE biplot analysis explained about 67.26 % of total variation and identified four genotypes (ICPLs 20094, 20106, 20098, 20115) as the most stable and resistant to SMD. Three genotypes (ICPLs 20096, 20107, 20110) showed moderately stable performance against SMD. These genotypes should be included in pigeonpea breeding programs as additional sources of resistance to SMD.

BackgroundPhytophthora blight caused by Phytophthora cajani is an emerging disease of pigeonpea (Cajanus cajan L.) affecting the crop irrespective of cropping system, cultivar grown and soil types. Current detection and identification methods for Phytophthora species rely primarily on cultural and morphological characteristics, the assessment of which is time-consuming and not always suitable. Sensitive and reliable methods for isolation, identification, zoospore production and estimating infection severity are therefore desirable in case of Phytophthora blight of pigeonpea.ResultsIn this study, protocols for isolation and identification of Phytophthora blight of pigeonpea were standardized. Also the method for zoospore production and in planta infection of P. cajani was developed. Quantification of fungal colonization by P. cajani using real-time PCR was further standardized. Phytophthora species infecting pigeonpea was identified based on mycological characters such as growth pattern, mycelium structure and sporangial morphology of the isolates and confirmed through molecular characterization (sequence deposited in GenBank). For Phytophthora disease development, zoospore suspension of 1 × 105 zoospores per ml was found optimum. Phytophthora specific real-time PCR assay was developed using specific primers based on internal transcribed spacer (ITS) 1 and 2. Use of real-time PCR allowed the quantitative estimation of fungal biomass in plant tissues. Detection sensitivities were within the range of 0.001 pg fungal DNA. A study to see the effect of elevated CO2 on Phytophthora blight incidence was also conducted which indicated no significant difference in disease incidence, but incubation period delayed under elevated CO2 as compared to ambient level.ConclusionThe zoospore infection method for Phytophthora blight of pigeonpea will facilitate the small and large scale inoculation experiments and thus devise a platform for rapid and reliable screening against Phytophthora blight disease of pigeonpea. qPCR allowed a reliable detection and quantification of P. cajani in samples with low pathogen densities. This can be useful in early warning systems prior to potential devastating outbreak of the disease.

Botrytis grey mould (BGM), caused by Botrytis cinerea Pers. Ex. Fr., is a destructive foliar disease of chickpea (Cicer arietinum L.) worldwide. Disease management through host-plant resistance is the most effective and economic option to manage this disease. The objective of this study was to identify new sources of resistance to BGM, validate their stability across environments and determine the magnitude of G Â E interaction. One hundred and nine chickpea genotypes with moderate levels of resistance (BGM severity 5.0 on a 1e9 scale) were selected from the preliminary evaluation of 412 genotypes including germplasm and breeding lines under controlled environmental conditions in 2004e2005 at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, India. In order to validate resistance stability, an 'International Botrytis Grey Mould Nursery' (IBGMN) was constituted with 25 genotypes and tested in multi-environments for BGM resistance at two locations (Gurdaspur and Pantnagar) in India for 4 years and two locations (Tarahara and Rampur) in Nepal for 3 years. Additive main effects and multiplicative interaction (AMMI) analysis showed significant genotype (G), environment (E) and G Â E interaction (p < 0.0001) with largest contribution by environment (47.36%). The first two principal component axes were significant, and contributed 48.21% to the total G Â E interaction. The AMMI biplot analysis allowed the selection of five genotypes ICCV 96859, ICCV 96853, ICCV 05604, ICCV 96852 and ICCV 05605 with low BGM severity (between 3.7 and 4.7 on 1e9 scale) and moderate stability. Genotype ICCV 96859 having least disease severity and moderate stability could be highlighted and exploited in chickpea resistance breeding programmes.

Background Fusarium wilt (Fusarium udum Butler), an important soil-borne disease of pigeonpea [Cajanus cajan (L.)], causes significant yield losses across the major pigeonpea production regions. Widespread and high diversity in F. udum hampers the breeding for pigeonpea wilt resistance. The study aimed to elucidate the pathogenic diversity and distribution of F. udum variants in major pigeonpea growing regions of India. Results The roving survey was conducted in major pigeonpea-growing states of India to collect the F. udum isolates. Pathogenic variability of 60 F. udum isolates which are selected from diverse geographical locations and pathogenicity test were performed against 11 pigeonpea host differentials cultivars [ICP 8858, ICP 8859, ICP 8862, ICP 8863, ICP 9174, C 11, BDN 1, BDN 2, LRG 30, ICP 2376 and Bahar (ICP 7197)]. The current study indicated distribution of F. udum isolates into nine variants (0, 1, 2, 3, 4, 5, 6, 7 and 8). Variant-2 and 3 were found to be widespread and predominant in most pigeonpea producing regions. Variant-7 (Karnataka) and Variant-8 (Madhya Pradesh and Maharashtra) were found highly virulent, as most of the host differentials were susceptible to these variants. Three host differential cultivars namely ICP 9174, BDN-2 and Bahar (ICP 7197) were found resistant to most of the F. udum isolates. Conclusion The present study generated significant information in terms of variants of F. udum which could be used further for the deployment of location-specific wilt resistant cultivars for optimized disease-management strategies. Study is also useful for development of broad-based wilt resistant cultivars to curtail the possible epidemics.

Pigeonpea (Cajanus cajan (L.) Millsp.) is the most important protein rich grain legume crop being cultivated worldwide. During surveys (2010 through 2012) conducted in major pigeonpea growing states in southern and central India (Andhra Pradesh, Karnataka, and Maharashtra), rapid mortality of pigeonpea plants was observed. This occurred in all of the surveyed areas with disease incidence of 20 to 60% irrespective of cultivar and crop growth stage. Symptoms included chlorosis, drooping and rolling of the leaves followed by rapid mortality of whole plant. Pinkish growth on infected stems and branches was observed and the inner layer of the infected stem had brown discoloration. Xylem vessels of the infected plants were healthy and did not show any blackening. Isolations from infected stem tissues consistently yielded cultures of Fusarium sp. on potato dextrose agar (PDA) medium. Monoconidial isolation from three separate isolates was used to establish pure cultures. The morphological characters of the fungus were consistent with descriptions in Fusarium keys (1) for Fusarium acuminatum (Ellis & Everhart). The mean colony growth was 86 mm after 7 days, with white aerial mycelium developing brownish pigmentation in the center on PDA. The dorsal side of the colony had rose to burgundy pigmentation. Macroconidia were broadly falcate with 3 to 5 septa, and were 3 to 8 × 39 to 64 μm. Microconidia were absent and chlamydospores formed in chains of 20 to 50 μm. Koch's postulates were established on seedlings of pigeonpea (cv. ICP 7119) using root dip inoculation of 10-day-old seedlings. The roots were immersed in a conidial suspension (6 × 106 conidia/ml) for 2 to 3 min; the control plants' roots were immersed in sterilized distilled water in a beaker. Inoculated seedlings were transplanted into pre-irrigated pots (12 cm) containing sterilized vertisol and sand (3:1). Five seedlings were used for each of three replications. Inoculated plants were kept in the greenhouse at 28 ± 2°C and irrigated with sterilized water. Inoculated plants developed symptoms identical to those observed in the field and disease incidence reached 100% within 96 h after inoculation. The experiment was conducted twice with two independent sets of plants. No symptoms were observed in water-inoculated control plants. The rDNA internal transcribed spacer (ITS sequence) was amplified with ITS1 and ITS4 primers (4). The amplicons of both forward and reverse (438 bp) were sequenced and submitted to GenBank (Accession No. JX177431). A BLASTn search revealed 100% sequence similarity to the nucleotide sequence of F. acuminatum (Ellis & Everhart) (GenBank Accession No. HQ443205). To our knowledge, this is the first report with confirmed molecular identification of F. acuminatum on pigeonpea. Occurrence of F. acuminatum on various plant species have been reported by Summerell et al. (3). Presence of F. acuminatum from soils of pigeonpea fields have been reported; however, no information on location, symptoms, plant mortality, and identification of pathogen has been provided (2). References: (1) J. F. Leslie and B. A. Summerell. Pages 122-123 in: The Fusarium Laboratory Manual. Blackwell Publishing Professional, Hoboken, NJ, 2006. (2) A. P. Singh and S. N. Bhargava. Phytopathol. Z. 100:300, 1981. (3) B. A. Summerell et al. Fungal Diversity 46:1, 2011. (4) T. J. White et al. Pages 315-322 in: PCR protocols: Guide to Methods and Applications, San Diego, Academic Press, 1990.

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