Cold tolerance at the germination stage of rice: methods of evaluation and characterization of genotypes

Abstract

Rice cold tolerance at the germination stage is important in Rio Grande do Sul (RS) where temperatures below 15°C prevent or reduce germination and plant establishment in early sowings. The present study aimed at identifying an adequate method for cold tolerance evaluation of the rice germination stage and at verifying the variability among 24 rice genotypes of different origins. Cold tolerance was evaluated in experiment I, germination under two conditions: 13°C for 28 days and 28°C for seven days, and in experiment II, germination under 28°C for 72 hours, 13°C for 96 hours and again 28°C for 72 hours. In experiment I measured characteristics were germination index, percentage of seeds with coleoptile length superior to 5 mm and percentage of reduction in coleoptile length due to cold. In experiment II the measured characteristic was coleoptile regrowth after the cold period. Cold tolerance varied among genotypes studied in both experiments, but only the percentage of reduction in coleoptile length and coleoptile regrowth allowed a better distinction between the tolerant checks and the susceptible one. In general, genotypes belonging to the Japonica subspecies presented higher cold tolerance than Indica, but there was variability within subspecies. The most adequate method of evaluation of cold tolerance is through percentage of reduction in coleoptile length and coleoptile regrowth. Among Japonica genotypes, Quilla 64117 and Diamante presented the highest cold tolerance, and among Indica, cultivars BR-IRGA 410 and IRGA 416 were the most cold tolerant at the germination stage. Key words: Oryza sativa L., low temperature, variability, Indica and Japonica subspecies TOLERÂNCIA AO FRIO NO ESTÁDIO DE GERMINAÇÃO EM ARROZ: MÉTODOS DE AVALIAÇÃO E CARACTERIZAÇÃO DE GENÓTIPOSRESUMO: A tolerância ao frio em arroz no estádio de germinação é importante no Rio Grande do Sul (RS) onde temperaturas abaixo de 15°C impedem ou reduzem a germinação e o estabelecimento das plantas em semeaduras precoces. O presente trabalho teve por objetivos identificar uma metodologia adequada para avaliação da tolerância ao frio na germinação em arroz e verificar a variabilidade existente entre 24 genótipos de arroz de diferentes origens. A tolerância ao frio foi avaliada em dois experimentos: experimento I, com germinação sob duas condições: 13°C por 28 dias e 28°C por sete dias, e experimento II, com germinação a 28°C por 72 horas, 13°C por 96 horas e novamente a 28°C por 72 horas. No experimento I as características medidas foram o índice de germinação, porcentagem de sementes com coleóptilo superior a 5 mm e porcentagem de redução no comprimento do coleóptilo devido ao frio. No experimento II a característica medida foi o recrescimento do coleóptilo após o período de frio. Houve variabilidade para tolerância ao frio entre os genótipos estudados em ambos os experimentos, mas apenas a porcentagem de redução no comprimento do coleóptilo e o recrescimento do mesmo permitiram melhor distinção entre as testemunhas tolerantes e a sensíve...

Cold tolerance evaluation in Chilean rice genotypes at the germination stage

“…In general, cold treatment induced a decrease in coleoptile length in all the evaluated varieties and genotypes. The reduction of coleoptile growth under low temperatures observed in the present study was also observed by other authors (Castillo and Alvarado, 2002;Cruz and Milach, 2004;Sharifi and Aminpanah, 2010). Low temperatures affect germination in the activation stage and postgermination growth (Yoshida, 1981).…”

“…Cold tolerance at the rice germination stage was evaluated according to a protocol by Cruz and Milach (2004), which was modified. Germination occurred in magenta vessels with 100 g of vermiculite moistened with 100 mL of distilled water.…”

“…To address this problem, many methodologies have been developed to evaluate cold tolerance in rice at the germination stage: germination index at 13 °C for 28 d, coleoptile growth at 13 °C for 3 d, and coleoptile regrowth at 28 °C for 4 d (Cruz and Milach, 2004); imbibition rate, germination rate, germination index, root length, shoot length, and seed vigor at 14 °C for 23 d (Wang et al, 2009); germination coefficient at 10, 13, and 15 °C (Baruah et al, 2009); germination rate, coleoptile length, and radicle length at 13 and 17 °C for 28 d (Sharifi and Aminpanah, 2010). Cold tolerance evaluated by Cruz and Milach (2004) is a good approximation to assess cold tolerance at the germination stage because they considered the coleoptile reduction and coleoptile regrowth after cold. This experiment allowed identifying parents and crosses with high cold tolerance.…”

“…Therefore, the evaluation of genotypes to detect high cold tolerance at the germination stage could be very important to improve rice varieties in Chile. The present study proposes evaluating cold tolerance at the germination stage for experimental lines from the Rice breeding Program of INIA Chile based on Cruz and Milach's (2004) methodology and multivariate analysis by Bosetti et al (2012).…”

Physiological and Molecular-Genetic Evaluation of Rice Breeding Resources on Cold Tolerance for Creating New Varieties for the Northern Zone of Rice Cultivation

“…According to (da Cruz and Milach, 2004), by the change of the length of the coleoptile alone, it is possible to identify a clear difference between cold sensitive and cold-tolerant genotypes (Cruz et al, 2006).…”