Grain mold and downy mildew are important biotic constraints to grain sorghum (Sorghum bicolor) production worldwide and are best managed through host plant resistance. A sorghum mini-core collection composed of 242 germplasm accessions developed from a core collection of 2,246 landrace accessions from 58 countries was evaluated to identify sources of grain mold and downy mildew resistance. Of the 242 accessions, 140 that flowered during the rainy season (the other 102 accessions were photoperiod sensitive) were screened for grain mold resistance in a grain mold nursery under field epiphytotic conditions during 2007 and 2008. All 242 accessions were screened for downy mildew in the greenhouse using a sandwich inoculation technique. Fifty accessions were resistant to grain mold (≤10% mean severity). These resistant accessions represented four basic and six intermediate races of sorghum that originated from 21 countries and exhibited considerable diversity for agronomic and morphological traits. Downy mildew resistance (mean incidence ≤10%) was observed only in six (IS 28747, IS 31714, IS 23992, IS 27697, IS 28449, and IS 30400) of the 242 accessions. One accession, IS 23992, exhibited resistance to both the diseases. The morphologically and agronomically diverse accessions that are resistant to grain mold or downy mildew should be useful to sorghum disease resistance breeding programs.

Fusarium species are dominant within the sorghum grain mold complex. Some species of Fusarium involved in grain mold complex produce mycotoxins, such as fumonisins. An attempt was made to identify Fusarium spp. associated with grain mold complex in major sorghum growing areas in India through AFLP based grouping of the isolates and further confirmation of the species by sequencing part of α-Elongation factor gene and comparing the sequences with that available in NCBI database. The dendrogram generated from the AFLP data clustered the isolates into 5 groups. Five species of Fusarium -F. proliferatum, F. thapsinum, F. equiseti, F. andiyazi and F. sacchari were identified based on sequence similarity of α-Elongation factor gene of the test isolates with those in NCBI database. Fusarium thapsinum was identified as predominant species in Fusarium -grain mold complex in India and F. proliferatum as highly toxigenic for fumonisins production. Analysis of molecular variance (AMOVA) revealed 54% of the variation in the AFLP patterns of 63 isolates was due to the differences among Fusarium species and 46% was due to differences among the strains within a species.

Rust, caused by the fungus Puccinia substriata var. indica, is one of the most important production constraints of pearl millet worldwide, leading to grain yield losses of up to 76 % as well as major losses in fodder yield and quality. Here, we report the development of a linkage map integrating Diversity Arrays Technology (DArT) markers and simple sequence repeat (SSR) markers, using this to identify quantitative trait loci (QTLs) for pearl millet rust resistance. Genotyping data from 256 DArT and 70 SSR markers on 168 F 7 recombinant inbred lines from cross 81B-P6 9 ICMP 451-P8 were used to construct a linkage map comprised of 286 loci (229 DArT and 57 SSR markers) spanning a total length of 740.3 cM (Haldane) with an average adjacent marker distance of 2.7 cM. Linkage group 7 (LG7) (153.5 cM) was the longest and LG6 the shortest (45.0 cM). The map was used to identify a major QTL for rust resistance with an LOD score of 27 on LG1, which explained 58 % of the observed phenotypic variation. In addition, two putative modifiers of small effect were detected, one each on LG4 and LG7. The novel rust resistance QTL identified on LG1 is thought to confer a durable slow-rusting phenotype, which is still effective in India more than 20 years after it was first deployed in the previously popular single-cross hybrid MH 179 (ICMH 451). The flanking markers reported here provide a framework for marker-assisted selection and possible future map-based cloning of this resistance gene.

Downy mildew, caused by Sclerospora graminicola, is a major pathogen of pearl millet (Pennisetum glaucum) in Asia and Africa. So development of resistant cultivars has been a major goal of national and international breeding programs. Stability of resistance in pearl millet lines developed at ICRISAT was studied through a collaborative International Pearl Millet Downy Mildew Virulence Nursery (IPMDMVN). The reactions to downy mildew of 11 pearl millet lines at 17 locations in India, Burkina Faso, Mali, Niger, and Nigeria from 1995 to 1999 were recorded. Disease incidence varied significantly among lines, locations, and years. The tested pearl millet lines exhibited significant differential resistance. Resistance in lines IP 18292, IP 18293, 700651 and P 310-17 was most stable regardless of the location or season. Analysis of the variation in resistance also suggested that the resistance in IP 18292 and IP 18293 was variable and depended on the locations and years, while the resistance in 700651 and P 310-17 was highly stable across locations and over years. The latter two lines could prove to be the most valuable sources of downy mildew resistance. The results also revealed significant differences in S. graminicola populations at different locations, with the highest disease at Bagauda (Nigeria) and Durgapura (India) and lowest from Coimbatore and Aurangabad (India). Based on the reaction of the 11 pearl millet lines, the 17 S. graminicola populations were grouped into six putative pathotypes (undefined populations closer to races). r

Sclerospora graminicola, the causal agent of downy mildew in pearl millet, is well-known for variation in its virulence pattern. Nine single-zoospore isolates (Sg 026-Z-1 to Sg 026-Z-9) derived from an oosporic isolate Sg 026 from a pearl millet F1 hybrid cultivar Nath 4209 grown in a farmer's field in a village, Veelad, in Maharashtra state, India, and three controls (Sg 026, Field-1, and Field-2) were evaluated for their virulence in two experimental runs in a greenhouse. The isolates were maintained on pot-grown seedlings of a highly susceptible pearl millet line, 7042S, in a greenhouse through asexual (sporangial) generations. Pot-grown seedlings of six pearl millet potential differential lines/cultivars (7042S, NHB 3, MBH 110, ICMH 451, 843B, and 852B) were spray-inoculated with a sporangial suspension (5 × 105 sporangia ml-1) and maintained in a greenhouse at 25 ± 2°C. Data were recorded for latent period (days) and disease incidence (%), from which a virulence index (incidence × latent period-1) was calculated to quantify disease-causing potential of isolates. Results indicated significant variation in latent period, incidence, and virulence index among isolates. The isolates were classified into four distinct pathotype groups based on their virulence indices on six pearl millet lines. Because of the significant variation for virulence in the S. graminicola population infecting Nath 4209, it is recommended that the hybrid be regularly monitored for downy mildew infection in farmers' fields, and be replaced by a resistant cultivar that is genetically unrelated to the parental lines of Nath 4209. This will help delay or avoid development of downy mildew epidemics and the resulting heavy loss to pearl millet farmers in the region.