Screening cotton genotypes for seedling drought tolerance

The objectives of this study were to adapt a screening method previously used to assess seedling drought tolerance in cereals for use in cotton (Gossypium hirsutum L.) and to identify tolerant accessions among a wide range of genotypes. Ninety genotypes were screened in seven growth chamber experiments. Fifteen-day-old seedlings were subjected to four 4-day drought cycles, and plant survival was evaluated after each cycle. Three cycles are probably the minimum required in cotton work. Significant differences (at the 0.05 level or lower) among entries were obtained in four of the seven experiments. A "confirmation test" with entries previously evaluated as "tolerant" (high survival) and "susceptible" (low survival) was run. A number of entries duplicated their earlier performance, but others did not, which indicates the need to reevaluate selections. Germplasms considered tolerant included: `IAC-13-1', `IAC-RM4-SM5', `Minas Sertaneja', `Acala 1517E-1' and `4521'. In general, the technique is simple, though time-consuming, with practical value for screening a large number of genotypes. Results from the screening tests generally agreed with field information. The screening procedure is suitable to select tolerant accessions from among a large number of entries in germplasm collections as a preliminary step in breeding for drought tolerance. This research also demonstrated the need to characterize the internal lack of uniformity in growth chambers to allow for adequate designs of experiments. Os objetivos desta pesquisa foram adaptar para o algodoeiro (Gossypium hirsutum L.) técnica de seleção previamente usada para avaliar tolerância à seca em plântulas de cereais e identificar acessos tolerantes entre uma gama de germoplasmas. Noventa diferentes genótipos foram avaliados em sete experimentos em câmara de crescimento. Plântulas de 15 dias de idade foram submetidas a ciclos de estresse hídrico de 4 dias e os índices de sobrevivência foram avaliados para cada ciclo. Três ciclos são o mínimo para se trabalhar com algodoeiro. Diferenças significativas (P < 0,05%) entre acessos foram obtidas em quatro dos sete experimentos. Um teste de confirmação foi executado, composto de entradas previamente classificadas como "tolerantes" (alta sobrevivência) e "suscetíveis" (baixa sobrevivência). Um número de entradas duplicou seu desempenho anterior mas outras não, o que indicou a necessidade de reavaliar as seleções. Em geral, a técnica é simples, embora exigente em tempo,