ABSTRACT:
The purple blotch is one of the most limiting diseases of the onion, and genetic resistance is most feasible way to control the disease. the aim of this study was to evaluate the reaction of onion genotypes to alternaria porri in the field. sixty four genotypes (cultivars, populations and lines of the embrapa breeding program) were evaluated under conventional tillage system. as a control were used the resistant population cnph 6342 and the susceptible male-fertile line 420. the crop was planted by direct sowing method with population of 500,000 plants per hectare. the experimental design was randomized blocks with five replications. plots consisted of six longitudinal rows on the seedbed, spaced 15 cm (total area of 0.9 m²). the disease occurred naturally in the field, and severity was evaluated on ten plants per plot at 80, 110 and 140 days after sowing. yield and the average mass of marketable bulbs (diameter ≥35 mm) was assessed in only 45 genotypes, which exhibited adaptation to local climate conditions and adequate bulbification. 'crioula mercosul', '446', 'bola precoce', 'juporanga l2', 'caeté', 'rainha', 'dourada', 'juporanga l7', 'cnph 6342', 'crioula alto vale' and 'roxa do barreiro' showed greater resistance to the pathogen, with area under the disease severity-progress curve (audspc) below 437.33, while the male-fertile line 420 presented aacpsd of 1177.94. the genotypes 'brs 367' and 'shinju', in turn, associated high productivity of marketable bulbs and moderate disease resistance, with yields greater than 43.9 t/ha and audspc below 567.28, these being considered the most tolerant genotypes to purple blotch.
Keywords:
Alternaria porri; plant breeding; resistance.
