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Inheritance of Partial Resistance to Blast in Indica Rice Cultivars

Jiangsu Academy of Agric. Sci., Nanjing, Peoples' Republic of China

D. J. Mackill^* and J. M. Bonman

Int. Rice Res. Inst., P. O. Box 933, Manila, Philipppines

^* Corresponding author.

The blast fungus (Pyricularia oryzae Car.) is a major cause of yield loss in rice (Oryza sativa L.). Partial or field resistance has received much attention as a means of conferring durable blast resistance. Previous inheritance studies of partial resistance have used japonica rices. The primary objective of this study was to determine the inheritance of partial resistance to leaf blast measured by lesion number (LN) and lesion size (LS) in crosses involving two indica rice cultivars with high partial resistance (‘IR36’ and ‘Milyang 42’) and two with low partial resistance (‘IR50’ and ‘Milyang 57’). Greenhouse-grown plants at the partially extended sixth-leaf stage were inoculated with a conidial suspension derived from a monoconidial isolate. Broad-sense heritability for selection based on a single plant ranged from 0.20 to 0.50 for LN and 0.35 to 0.67 for LS. The narrow-sense heritability ranged from 0.18 to 0.38 for LN and 0.30 to 0.43 for LS. Significant (P < 0.01) differences between F₃ families selected from the most resistant and most susceptible F₂ plants were observed for crosses between resistant and susceptible parents for both LN and LS. The F₂ populations also were grown in the field blast nursery under natural infection, and the area under the disease progress curve (ADPC) was calculated based on percent diseased leaf area from 22 to 39 d after seedling emergence. The broad-sense heritability for ADPC was 0.40 and 0.30 for two resistant x susceptible crosses and 0.14 for a resistant x resistant cross. The results indicate that heritability for partial resistance to rice blast in these crosses is relatively low, and that selection for resistance should be effective if resistance levels can be assessed accurately.

Received for publication January 25, 1988.

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