Journal of Crop Breeding

Extended Abstract
Background: Rice is the second most important grain in the world after wheat and is considered one of the oldest crops. Although its cultivated area in the world is less than wheat, its production amount equals wheat. This plant is the main food of more than half of the world's people, with a per capita consumption of 50 kg. In many developing countries, the rice produced does not keep up with consumption due to population growth, and it is expected that this problem will become more acute in the future. Therefore, international organizations have tried to speed up breeding programs, and in this regard, the International Rice Research Institute (IRII) has paid special attention to rice-growing countries. In recent years, the spread of the system of rice cultivation twice a year, along with the risk of water shortage, has seriously limited the area under cultivation of late varieties, which have higher water consumption. Therefore, the development of semi-pure early and dormancy-resistant cultivars, with a shorter growth period and less water requirement, is one of the most important research priorities. The present research was carried out in the form of two experiments to study the compatibility and stability of pure early and short lines resulting from a cross between local cultivars and improved cultivars.
Methods: To study the adaptability and stability of promising early rice lines, expriments were conducted with a randomized complete block design in three replications during two crop years 2022 and 2023 in three regions (Deputy of the Country Rice Research Institute in Amol, Tankabon Rice Research Station and Goldasht Rice Research Station, Babol). The treatments included five pure early rice genotypes (70 days from sowing to 50% flowering) and short (85-90 cm) lines, the result of crossing between local cultivars and modified cultivars, along with two Kohsar and Tarem Mazand cultivars as controls. The studied traits included the number of days to 50% flowering, plant height (cm), the number of fertile tillers per plant, cluster length (cm), the number of full and empty seeds per cluster, 1000-seed weight (g), the percentage of full grain, and paddy yield. Stability analysis was performed using Lin and Binns (1991) and AMMI (Crosaa, 1990) methods. AMMI stability analysis calculations were performed using Biplot software (Yan et al., 2007). Statistical analysis of the data, including testing the normality of the data distribution, Bartlett's test to examine the homogeneity of the variance of the errors, and the composite analysis of variance, assuming the randomness of the year effect, were performed with SAS software version 9.4. The AMMI method was used for stability analysis using AMMISOFT version 1.0 software.
Results: The results of a two-year compound analysis of variance in three places showed that the effect of year was not significant on the traits of plant height, spike length, the percentage of seed filling, and the number of seeds, but it had a substantial effect on the other traits. The simple effect of location was not significant on all the traits, and the interaction effect of year × location was substantial on all traits, except for grain yield. Moreover, the simple effect of genotype was substantial for all the studied traits, except for the number of claws, the percentage of seed filling, and the number of empty seeds. While the interaction effect of year in genotype was significant on most traits, the interaction effect of location × genotype was substantial only on 1000-seed weight and seed filling percentage traits. The triple interaction effect of year × location × genotype was statistically significant on all traits. Line Z3 with 7493 kg/ha produced the highest yield in three regions in two years, which was significantly different from the other lines. The highest number of claws (20) belonged to the Z5 line, followed by the Z1, Z3, and Z4 lines, with 18.3, 18.3, and 18.2 cm, respectively. The Z2 line, along with two control varieties, was placed in the last group. The maximum length of the cluster belonged to the Tarem Awn variety (26.5 cm), followed by Z5 (26.4 cm) and Z4 (25.5 cm) lines, and the cluster length of other lines and Kohsar variety was about 24 cm. The highest number of full seeds in the cluster (144.4) was assigned to the Z4 line and the lowest amount to the two varieties of Tarem Rishek short and Kohsar, with 85.6 and 1.89 seeds in the cluster, respectively. The lowest number of hollow seeds (16) in this test was assigned to the Z1 line and the most to the Z4 line (27). The Z4 line contained more total number of seeds in the cluster (with an average of 171.4) than the others. The lowest total number of seeds in the cluster belonged to the two control cultivars Tarem Mazand and Kohsar (103.9 and 112.2 seeds, respectively). The highest 1000-seed weight belonged to the Kohsar variety (27.7 g), and other genotypes did not show significant differences. The highest seed filling percentage belonged to Z1 and Z2 lines with 87.5 and 86.0%, respectively. The Kohsar variety showed the lowest seed filling rate (79.8%), and the seed filling rate in the Tarem variety was 82.9%. The studied lines were between 79.4 and 83.8 days in terms of the number of days to flowering, similar to the Kohsar variety (79.4 days) and earlier than the short-bearded Tarem variety (88.4 days). According to the AMMI diagram, the two genotypes Z3 and Z4 showed high yields and stability in this experiment.
Conclusion: Genotypes Z3 and Z2 were selected as the first and second options, with yields of 7493 and 6508 kg/ha, respectively, along with yield stability, short height, and a growth period length almost similar to the early variety Koohsar.