Variation in pathogenicity among single-oospore isolates of Sclerospora graminicola, the causal organism of downy mildew in pearl millet

Thakur, R P and Shetty, K G (1993) Variation in pathogenicity among single-oospore isolates of Sclerospora graminicola, the causal organism of downy mildew in pearl millet. Plant Pathology, 42 (5). pp. 715-721. ISSN 1365-3059

PDF - Published Version Restricted to ICRISAT users only Download (1MB) | Request a copy

Abstract

Variation in pathogenicity (virulence and aggressiveness) of various single-oospore isolates of Sclerospora graminicola, the causal organism of downy mildew in pearl millet, was studied. Oospore isolates were maintained as sporangial progenies on the susceptible pearl millet genotype 7042-S through asexual generations. Twenty single-oospore isolates obtained from samples of oospore inocula from three locations (the ICRISAT Centre, Coimbatore, and Hisar) in India, were tested for pathogenicity on 7042-S. All the isolates were virulent on 7042-S and they varied considerably, between and within locations, in infection efficiency (11–44% infection). The S. graminicola populations from the ICRISAT Centre and Hisar were significantly more aggressive than those from Coimbatore. Considerable variation was found among the 10 single-oospore isolates from the ICRISAT Centre in infection efficiency and for latent period on a set of resistant and susceptible genotypes. Seven representative isolates, two each from the ICRISAT Centre (ICOS) and Coimbatore (CBOS), and three from Hisar (HSOS), exhibited variation in infection efficiency, sporangial production capacity, and oospore production rating on the susceptible genotypes 7042-S and NHB 3. A pathogenic fitness index (PFI) was calculated for these isolates as the product of the reciprocal of the latent period × percentage infected seedlings × log10 sporangia per cm2 leaf area × oospore production rating. Aggressiveness of these isolates, measured as PFI, varied greatly. CBOS-1 was the least aggressive with a PFI of 8·5 on NHB 3 and 69·6 on 7042-S; the PFI of the other isolates ranged from 81·1 to 370·5. Downy mildew resistance in three of the five known resistant lines (700651, P7-4 and 7042-R) was consistently effective against all 10 ICOS isolates, indicating that the resistance of these three lines is likely to be more stable, at least at the ICRISAT location, than that of the other two resistant lines.

Item Type:	Article
Divisions:	UNSPECIFIED
CRP:	UNSPECIFIED
Subjects:	Mandate crops > Millets
Depositing User:	Mr Charan Sai Ch
Date Deposited:	23 Oct 2011 11:03
Last Modified:	23 Oct 2011 11:03
URI:	http://oar.icrisat.org/id/eprint/3111
Official URL:	http://dx.doi.org/10.1111/j.1365-3059.1993.tb01557...
Projects:	UNSPECIFIED
Funders:	UNSPECIFIED
Acknowledgement:	The authors thank K. J. Leonard, S. B. King, and S. D. Singh for their useful comments on the manuscript, and V. P. Rao for his help in statistical analysis.
Links:	Author

View Statistics

Actions (login required)

View Item