Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
‣ The average percent loss has been noted in the range of 50.6 to 80.7 percent due to Alternaria
blight disease under Kharif conditions. However, the percent loss in oil has been shown in the
range of 21.6 to 32.3. To control the disease, total 4 sprays of mancozeb @ 0.3% at 10 day
interval have been found effective.
‣ A repository of about 5000 rice blast isolates was made from 30 locations in Indian Himalayas at
Hill Campus, Ranichauri. Blast pathogen population from the region was analyzed using molecular
markers and phenotypic assays. Most locations sampled and analyzed had distinct populations
with some containing one or a few lineages and others were very diverse. Within an
agroecological region migration appeared to be high. The structure of some populations could be
affected to some extent by sexual recombination.
‣ Magnaporthe grisea isolates derived from Eleusine coracana, Setaria italica and Echinochloa
frumentaceum collected from a disease screening nursery were cross compatible. The
chromosome number of each isolate was found to be six or seven. Similarity of karyotypes was
found among isolates with in a lineage though between lineages some variability was noticed. A
remarkable similarity between karyotypes of Eleusine coracana and Setaria italica was observed. All
of these isolates were fertile and mated with each other to produce productive perithecia. The
existing data however showed no evidence of genetic exchange among host-limited M. grisea
populations in Indian Himalayas.
‣ No strong relationship appeared between the number of virulences in a pathotyope and its frequency
of detection. The frequency of virulent phenotype to a cultivar and susceptibility of that cultivar in the
field did not correspond. The number of virulences per isolate was in general less than the number
of virulences per pathotype, which indicated predominance of isolates from pathotypes with fewer
virulences. There was a tendency for the pathotypes to have fewer virulences. The frequency of
virulence among rare pathotypes was higher than common pathotypes against all the differential
NILs, including two-gene pyramids. These rare pathotypes could be the potential source of
resistance breakdown of the novel resistance genes.
‣ Blast resistant gene Pi-2(t) appeared to have the broadest and Pi-1(t) the narrowest resistant
spectra. Compatibility to Pi-2 (t) gene did not appear to limit compatibilities with other resistant
genes. Loss of avirulence to all the five major gene tested may carry a serious fitness penalty.
Major gene Pi-2 and gene combination Pi-1,2 showed least compatibilities and hold promise
in managing blast in the region. In the overall Himalayan population, gene combinations in
general were effective at most locations. Combination of Pi-1+2 genes was effective at most
locations until the year tested. However, three gene pyramid [Pi-1(t) + Pi-2(t)+Pi-4(t)] resisted
infection at all locations.
‣ It was inferred that the pathotype composition of the blast pathogen composition in the Indian
Himalayas was very complex and diversifying the resistance genes in various rice breeding
programmes should prove to be a useful strategy for disease management.
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