ICRISAT Archival Report 2006 - The seedlings of success in the ...

Crossing was initiated for marker-assisted backcrossing programs to introgress downy mildew resistance QTLs from
several donor parents (including P1449-2, P310-17, ICMB 90111-P6, PRLT 2/89-33 and 863B-P2) into the genetic
backgrounds of several elite hybrid parental lines chosen by national program partners in India (including restorer
lines J 2340, H 77/29-2 and ICMR 01004 as well as seed parent maintainer lines HMS 7B, ICMB 93333, and ICMB
95444).
Output target 5A.5: Virulence changes in pearl millet DM pathogen populations determined (2009)
Activity 5A.5.1: Conduct field and laboratory studies to monitor the nature of virulence change in DM
pathogen populations
Milestone 5A.5.1.1: Ten to fifteen DM isolates each from Gujarat, Rajasthan, Maharashtra and Uttar Pradesh
characterized for pathogenicity and virulence (RPT/RS/KNR/RB, 2008)
Characterization of isolates of Sclerospora graminicola for pathogenicity and virulence: Isolates collected from
highly susceptible pearl millet cultivars during on-farm survey are characterized for pathogenicity and virulence.
Highly virulent isolates thus identified are used for screening breeding lines for developing downy mildew resistant
hybrid parental lines.
Pathogenic variation: Eleven isolates collected from five districts (Jamnagar, Anand, Kheda, Banaskantha and
Gandhinagar) of Gujarat during the on-farm survey of 1998−2005 were established on potted pearl millet seedlings
of 7042S in a glasshouse. The pathogenicity and virulence diversity of these isolates were determined by
inoculating the pot-grown seedlings of a set of eight host differential lines (P 7-4, P 310-17, 700651, 7042R, IP
18292, IP 18293, 852B and ICMP 451) and a susceptible check 7042S. The experiment was conducted with 11
isolates, 9 host differentials and 3 replications with 30−35 seedlings/replication in a completely randomized design
(CRD). The latent period 50% was recorded from 4 th day onwards after inoculation and disease incidence 2 weeks
after inoculation. Based on latent period 50% and disease incidence, virulence index (disease incidence × latent
period -1 ) was calculated to measure the quantitative virulence of the isolates. The results indicated that of the 11
isolates Sg 441 and Sg 445 (from Banaskantha) were the more virulent with mean incidence of 78−84% across 9
host differentials, and Sg 348 (from Anand) was the least virulent (26% incidence). The dendrogram based on the
virulence index using the Euclidean square distances (the average linkage cluster analysis) classified these isolates
(at 90% similarity coefficient) into four groups- Sg 200, Sg 348 and Sg 442 in Gr 1 (less virulent); Sg 432, Sg 438,
Sg 439, and Sg 440 in Gr 2 (moderately virulent); Sg 435 and Sg 437 in Gr 3 (virulent) and Sg 441 and Sg 445 in
Gr 4 (highly virulent). The isolate Sg 445 is currently being used to screen breeding lines targeted for Gujarat.
RP Thakur
Effectiveness of pathotypes mixture for screening breeding lines: Development of improved breeding lines as
potential parental lines (A-, B- and R-lines) of hybrids with high level of DM resistance has been the major research
focus at ICRISAT. These breeding lines are routinely screened against individual pathotypes in succession to
identify those with resistance to single or multiple pathotypes. Many times, a question is asked what if the pearl
millet lines could be evaluated against a mixture of pathotypes instead against individual pathotypes in order to
reduce time and save resources. To address this issue, an experiment was conducted to test the relative efficacy
mixture of two pathotypes - Sg 150 from Jalna, and Sg 212 from Durgapura along with the individual pathotypes
for screening pearl millet lines. Twelve pearl millet lines (P 7-4, P 310-17, 700651, 7042R, 852B, 834B, 843B, IP
18292, IP 18293, 863B, ICMB 03999 and S 2003-188) known for their differential reactions to these pathotypes
and two susceptible checks (7042S and ICMP 451) were used. Experiment was conducted in CRD with three
treatments of pathogen and 14 genotypes in 6 replications (one pot/replication with 35−40 seedlings). The
experiment was repeated to confirm the results. The results indicated that the pearl millet lines that were highly
susceptible to either or both pathotypes were also highly susceptible to pathotype mixture, and the lines that were
not highly susceptible to either of the pathotype had average susceptibility. Thus, the use of pathotype mixture
would serve the purpose of discarding the highly susceptible lines. However, screening against specific pathotypes
may provide more reliable data on resistance levels of the genotypes.
RP Thakur
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