Virulence Characterization of Single-Zoospore Isolates of Sclerospora graminicola from Pearl Millet

S. graminicola, the causal agent of downy mildew in pearl millet (Pennisetum glaucum), 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 3 controls (Sg 026, Field-1 and Field-2) were evaluated for their virulence in 2 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 6 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) 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) 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 4 distinct pathotype groups based on their virulence indices on 6 pearl millet lines. It is concluded that due to 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

Inheritance and Allelic Relationship among Downy Mildew Resistance Genes in Pearl Millet

Pearl millet downy mildew (DM), caused by Sclerospora graminicola is of serious economic concern to pearl millet farmers in the major crop growing areas of the world. To study the inheritance and allelic relationship among genes governing resistance to this disease, three DM resistant pearl millet lines (834B, IP 18294-P1 and IP 18298-P1) and one susceptible line (81B) were selected on the basis of disease reaction under greenhouse conditions against two isolates of S. graminicola (Sg 526-1 and Sg 542-1). Three resistant parents were crossed with the susceptible parent to generate F1s, F2s and backcrosses BC1P1 (susceptible parent × F1) and BC1P2 (resistant parent × F1) for inheritance study. To carry out test for allelism, the three resistant parents were crossed with each other to generate F1s and F2s. The different generations of these crosses were screened for disease reaction against two isolates Sg 526-1 and Sg 542-1 by artificial inoculation under greenhouse conditions. The segregation pattern of resistance in the F2s, and corresponding backcross generations revealed that resistance to DM is controlled by a single dominant gene in 834B and IP 18294-P1, and by two dominant genes in IP 18298-P1. Test for allelism inferred that single dominant gene for resistance in 834B is non-allelic to that governs resistance in IP 18294-1; whereas one of the two dominant genes for DM resistance in IP 18298-P1 against the test isolates is allelic to gene for DM resistance in 834B and second gene is allelic to the resistance gene present in IP 18294-P1

Effect of temperature on Rhizoctonia bataticola and dry root rot in chick pea

Chickpea dry root rot caused by Rhizoctonia bataticola (Taub.) Butler is a soil borne fungal pathogen causing significant yield losses due to change in environmental conditions. Influence of seven temperatures regimes (15°C, 20°C, 25°C, 30°C, 35°C, 40°C and 45°C) were tested on growth of R. bataticola isolates representing Madhya Pradesh, Karnataka, Maharashtra, Andhra Pradesh and Telangana states of India. The maximum mycelial growth was observed at 35ºC followed by 30 and 25ºC in all the isolates. The optimum temperature for dry root rot severity rating was at 35°C (8.5) followed by 30°C (7.9) followed by 25°C (7.0). Among the isolates, Telangana isolate was virulent and caused maximum disease severity

Inheritance and allelic relationship among gene(s) for blast resistance in pearl millet [Pennisetum glaucum (L.) R. Br.]

Six blast‐resistant pearl millet genotypes, ICMB 93333, ICMB 97222, ICMR 06444, ICMR 06222, ICMR 11003 and IP 21187‐P1, were crossed with two susceptible genotypes, ICMB 95444 and ICMB 89111 to generate F1s, F2s and backcrosses, BC1P1 (susceptible parent × F1) and BC1P2 (resistant parent × F1) for inheritance study. The resistant genotypes were crossed among themselves in half diallel to generate F1s and F2s for test of allelism. The F1, F2 and backcross generations, and their parents were screened in a glasshouse against Magnaporthe grisea isolates Pg 45 and Pg 53. The reaction of the F1s, segregation pattern of F2s and BC1P1 derived from crosses involving two susceptible parents and six resistant parents revealed the presence of single dominant gene governing resistance in the resistant genotypes. No segregation for blast reaction was observed in the F2s derived from the crosses of resistant × resistant parents. The resistance reaction of these F2s indicated that single dominant gene conferring resistance in the six genotypes is allelic, that is same gene imparts blast resistance in these genotypes to M. grisea isolates

Identification of genes controlling compatible and incompatible reactions of pearl millet (Pennisetum glaucum) against blast (Magnaporthe grisea) pathogen through RNA-Seq

Blast [Magnaporthe grisea (Herbert) Barr] is an economically important disease in Asian pearl millet production ecologies. The recurrent occurrence of blast in the past one decade has caused enormous strain on grain and forage production. Identification of resistance genes is an important step to develop durable varieties. The present study is the first attempt to use RNA-Seq to investigate the transcript dynamics in a pearl millet inbred ICMB 93333, which had a unique differential reaction to two isolates—Pg 45 (avirulent) and Pg 174 (virulent) of M. grisea. The inbred was inoculated by both isolates and samples taken at six different time intervals for genome-wide RNA-Seq experiment. The transcriptome results revealed the differential expression of more than 2,300 genes. The time-specific comparison showed activation or repression of specific genes in various pathways. Genes and transcriptions factors related to pathogenesis-related proteins, reactive oxygen species generating and its scavenging genes, cell wall defense, primary and secondary metabolic pathways, and signaling pathways were identified by comparing the host-plant compatible and incompatible interactions. The genes identified from this experiment could be useful to understand the host-plant resistance and design novel strategies to manage blast disease in pearl millet

Multiple shoots from the cultures of Morus indica var. Mysore local

Morus indica var. Mysore local commonly known as "Natikaddi" was extensively cultivated in traditional sericultural tracts of Karnataka. Nodal segments from tender lateral branches of three year old plants were inoculated onto Murashige and Skoog's/modified Murashige and Skoog's medium supplemented with various growth regulators. Effect of auxins and cytokinins either singly or in combination on the multiple shoot regeneration was studied. BAP supplemented medium was found to be best for maximum number of multiple shoots. In vitro regenerated shoots were rooted on soilrit mixture fed with liquid 1/4 strength Murashige and Skoog's medium supplemented with either IBA or NAA. About 55 of survival of tissue cultured plants in field condition was recorded. The efficient protocol for multiple shoot induction thus developed can be further exploited through biotechnological approaches for genetic improvement of var. Mysore local. © 2009 Society for Biology and Biotechnology

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Not AvailableBiochemical nature of 25 isolates of Alternaria helianthi were characterized based on production of total sugars, total proteins,total free amino acids and phytotoxins. The estimation of all parameters reflected significant variation among all. The isolate Ah-25 produced maximum concentration of total sugar (13.28 mg), while minimum concentration was noticed in Ah-13 (3.10 mg). Similarly, the total proteins content was found highest in the isolate Ah-25 (21.43 mg) and lowest with the isolate Ah-15 (9.53 mg). Among the isolates, the total free amino acids ranged between 5.67 mg (Ah-15) to 21.24 mg (Ah-21). The phytotoxicity of the crude toxin was tested by adopting detached leaf technique at different concentrations.None of the tested isolates have produced symptoms at 50 ppm concentration. However, the typical symptoms of necrotic lesions were observed at 100 ppm with nine isolates (Ah-1, Ah-2, Ah-4, Ah-7, Ah-12, Ah-17, Ah-21, Ah-24 and Ah-25). Further, the strains were found to vary in their biochemical composition between all the isolates under the study.Not Availabl

Fertility and Mating Type Frequency in Indian Isolates of Sclerospora graminicola, the Downy Mildew Pathogen of Pearl Millet

Sclerospora graminicola, the downy mildew pathogen of pearl millet, is an oomycetous obligate parasite which reproduces by both sexual and asexual means. Fertility and mating type frequencies were studied in 70 single-zoospore isolates (SZIs) obtained from seven representative oo-sporic isolates (Sg 021, Sg 048, Sg 110, Sg 139, Sg 149, Sg 152, and Sg 153) of S. graminicola collected from major pearl millet-growing states of India. Of the 70 SZIs tested for fertility according to oospore production potential, 62 were self-sterile and 8 were self-fertile, indicating the low occurrence of homothallism in the S. graminicola populations. The sexual mating type test of the 70 SZIs, conducted by pairing each isolate with the two standard mating type tester isolates PT2 (Mat A) and PT 3 (Mat B), revealed 28 (40.0%) isolates of Mat A, 33 (47.14%) of Mat B, 8 (11.43%) of both Mat A and Mat B, and 1 (1.43%) as unknown. The frequencies of Mat A and Mat B were in approximately equal proportions among the isolates tested, except in three parental isolates. Implications of these results in understanding the dynamic genetic structure of S. graminicola population and potential for evolution of new virulence in the pathogen are discussed

Inheritance of avirulence in Sclerospora graminicola, the pearl millet downy mildew pathogen

The inheritance of avirulence in S. graminicola was studied by hybridizing the isolates Sg 139-4 (Mat A), highly virulent, and Sg 110-9 (Mat B), avirulent, on a pearl millet (Pennisetum glaucum) genotype IP 18292 containing a downy mildew resistance gene Rsg1. Pot-grown seedlings of IP 18292 were inoculated with sporangial inocula generated from sexual spores (oospore) of the parental isolates and their F1, F2, BC1 and BC2 progenies and incubated at 25±2°C and >90% relative humidity in a greenhouse. Downy mildew incidence was recorded two weeks after inoculation. Avirulence was dominant over virulence and a single gene pair (AA/Aa) controlled avirulence in isolate Sg 110-9 to a corresponding resistance gene Rsg1 in IP 18292. The pattern of segregation of virulence:avirulence suggested the presence of a gene-for-gene interaction between S. graminicola and P. glaucum