Characterization of the resistance to mechanical damage by Tagosodes orizicolus (Muir) (Homoptera:Delphacidae) in twelve rice cultivars (Oryza sativa)
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Abstract
Tagosodes orizicolus (Muir) is an important pest of rice in Latin America because it transmits the Hoja Blanca virus and causes mechanical damage to the plant through its feeding and oviposition. In Colombia, all rice varieties developed through the ICA-CIATFEDEARROZ Agreement are reported as resistant to «sogata», the common name of the insect. However no efforts to diversify the resistance sources have been mute, and commercial varieties and advanced lines are being used as donors of resistance. Given the narrow genetic basis of the resistant sources, this study was undertaken to identify the resistant parents or donors more frequently used in Latin America, and to establish the heritability mode of Makalioka and Mudgo. The materials were characterized as resistant or susceptible based on free-choice and no-choice tests and, on the survival and oviposition of the insect. Two groups resulted: Mudgo, Amistad 82, IRAT 120, IRAT 124, and Makalioka as resistant materials; and Chianan 8, Colombia 1, Bluebonnet 50, IR 8 (ICA), IR 8 (IRRI), Tetep and Cica 8 as susceptible materials. It was found that the damage caused by the insect to the materials was associated with insect survival, oviposition, and egg hatching. To determine heritability, two parents were selected: Makalioka and Mudgo, which were crossed with IR 8. F, and F, populations were also evaluated based on the free-choice test with an alternative. Finally, based on the crosses' reactions to the insect damage and comparing them with the parents, a genetic model of resistance is proposed for Mudgo and Makalioka to be a single dominant gene of the homozygous form (AA) accompanied by a modifier gene which interferes in a greater or lesser intensity with the resistance expression (bb>Bb>BB) depending on the material and on the exposure time of the plant to the insect. For Mudgo the recessive homozygous form (bb) accelerates the expression of the susceptible phenotype and for Makalioka the homozygous dominant form (BB) which delays the expression of the susceptible phenotype.
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