Line (five) × tester (two) analysis was conducted to determine good parents and the nature of gene action governing yield and its component traits in rice. The line × testers showed significant differences for all traits except for number of spikelets per panicle and hundred grain weight. Parents with low × high general combining ability (GCA) effects resulted in heterotic hybrid combination like the IR62829A/IR57301-158-1R. A low × low GCA gave the best heterotic combination i.e. IR68888A/'Sepidroud'. The study showed GCA to only identify better parental lots and it will be unwise to discard the low GCA types. Predominance of dominance gene action for all the traits studied except for flag leaf width and number of spikelets per panicle suggests heterosis breeding must be strongly pursued for exploitation of the yield advantage over the inbred varieties.

Poor seedling establishment in rice is one of the problems in Guilan province as the second most important rice-growing locations in Iran. The aim of this study was to evaluate the contamination occurrence of rice seed in five locations of Guilan province to seed-borne fungi and their effects on germination characteristics. Five seed sample of Hashemi variety obtained from leading farmers from each location, and their germination characteristics and the rate of contamination to Fusarium moniliforme, Bipolaris oryzae, Aspergillus niger, A. flavus, Penicillium sp., Alternaria padwickii was evaluated using the PDA and standard blotter methods. The assessment results showed that among the seed-borne fungi, two species A. niger and A. flavus exhibited the highest severity in both methods. Samples from Rasht and Zeybaknar locations showed the most contamination to A. flavus and A. niger. A positive and significant linear relationship was observed between daily precipitation and relative humidity with severity of A. flavus and A. niger fungus. A. niger, A. padwickii, daily precipitation and average minimum temperature had the most influence on germination characteristics. Among the studied factors, A. niger had high negative impact compared to other factors on all rice seed germination characteristics. Among the study locations, quality of seeds in Rostam-Abad in terms of germination percentage, germination rate, germination uniformity and electrical conductivity had the best state. The results of this study showed that the low precipitation and low daily average humidity along with higher number of sunshine hours in the Rostam-Abad caused reduction in activity and abundance of fungi, led to improve the quality of produced seed.

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As an abiotic stress, adverse germination temperatures cause serious disruptions in physiological and biochemical processes involved in seed germination. Using a factorial experiment, we examined the effects of different seed priming treatments on enzymatic and biochemical performance of rice seeds germination under different temperatures. The results showed that the enzymatic and biochemical activities of all rice genotypes are affected by seed priming agent, especially under low germination temperature. At 15°C, seed priming with ascorbic acid was found the best agent for amylase, α-amylase, soluble sugars, catalase, peroxidase, ascorbate peroxidase, superoxide dismutase respectively with 0.095, 0.047, 29.4, 0.049, 10.9, 1.24 and 2.63 units in NORIN-22 genotype and for protease and soluble proteins with 0.058 and 0.79 units in IRON-70-7053-7 genotype. Among the enzymatic activities, at low germination temperature, the superoxide dismutase and at optimum and high germination temperature, the activity of catalase, peroxidase and Protease were the most important enzymatic activity in occurrence of germination potential in terms of seedling length, vigour index, normal seedling percentage and germination rate. Under priming agents, the highest changes in normal seedling percentage were observed at low and optimum germination temperature by ascorbic acid priming in Hashemi (216.9%) and NORIN-22 (13.2%) genotypes, and at high germination temperature under KCl priming in Hashemi genotype (39.4%).

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