Hybrid seed set on the female line depends primarily on its flowering synchronization with the restorer line (R), therefore, the sowing of male and female lines must be planned properly to achieve this. Field experiments on different sowing dates (May 1st, May 15th, and May 30th) of R lines (Giza 178R, Giza 179R, and Giza 181R) and cytoplasmic male sterile (CMS) lines (IR69625A, IR70368A, IR58025A, K17A, and G46A) were carried out at the farm of Sakha Agricultural Research Station, Kafr El-Sheikh, Egypt during 2019 and 2020 to study the effect of sowing dates on flowering synchronization in hybrid rice. The results indicated that the synchronization of flowering between CMS lines and R lines has highly significant effects on the days to 50% heading, number of leaves, effective accumulated temperature (EAT), plant height, panicle exertion percentage, panicle length, number of fertile panicles, panicle weight, seed set percentage, harvest index and seed yield of hybrid rice. The highest seed yield (1.72 and 1.41 t ha−1, respectively in 2019 and 2020) was recorded from the sowing date May 1st and the hybrid combination of Giza 178R × IR58025A (2.06 and 2.12 t ha−1 in 2019 and 2020, respectively). The grain yield had a significant and highly significant positive correlation with the plant height (cm), panicle exertion percentage, panicle length, number of panicles plant−1, panicle weight, seed set percentage, and harvest index. In Egypt, May 1st is the best time for the synchronization of hybrid rice lines and a combination of Giza 178R × IR58025A may be recommended for better performance.
Cytoplasmic male sterility (CMS) provides an irreplaceable strategy for commercial exploitation of heterosis and producing high-yielding hybrid rice. The exogenous application of plant growth regulators could improve outcrossing rates of the CMS lines by affecting floral traits and accordingly increase hybrid rice seed production. The present study aimed at exploring the impact of growth regulators such as gibberellic acid (GA3), indole-3-acetic acid (IAA), and naphthalene acetic acid (NAA) on promoting floral traits and outcrossing rates in diverse rice CMS lines and improving hybrid rice seed production. The impact of foliar applications of growth regulators comprising GA3 at 300 g/ha or GA3 at 150 g/ha + IAA at 50 g/ha + NAA at 200 g/ha versus untreated control was investigated on floral, growth, and yield traits of five diverse CMS lines. The exogenously sprayed growth regulators, in particular, the combination of GA3, IAA, and NAA (T3) boosted all studied floral, growth, and yield traits in all tested CMS lines. Moreover, the evaluated CMS lines exhibited significant differences in all measured floral traits. L2, L3, and L1 displayed the uppermost spikelet opening angle, duration of spikelet opening, total stigma length, style length, stigma brush, and stigma width. In addition, these CMS lines exhibited the highest plant growth and yield traits, particularly under T3. Consequently, exogenous application of GA3, IAA, and NAA could be exploited to improve the floral, growth, and yield traits of promising CMS lines such as L2, L3, and L1, hence increasing outcrossing rates and hybrid rice seed production.
In rice, cytoplasmic male sterility (CMS) represents an irreplaceable strategy for producing high-yielding hybrid rice based on the commercial exploitation of heterosis. Thereupon, enhancing floral traits and outcrossing rates in CMS lines increase hybrid seed production and ensure global food security. The exogenous application of cyanobacteria could enhance outcrossing rates in CMS lines and, accordingly, hybrid rice seed production. In the present study, we aimed at exploring the impact of cyanobacteria implementation such as Anabaena oryzae, Nostoc muscorum, and their mixture to promote the floral traits, outcrossing rates, and seed production in hybrid rice. The impact of cyanobacteria (Anabaena Oryza (T2), Nostoc muscorum (T3), and their combination (T4) versus the untreated control (T1) was investigated for two years on the growth, floral, and yield traits of five diverse CMS lines, namely IR69625A (L1), IR58025A (L2), IR70368A (L3), G46A (L4), and K17A(L5). The evaluated CMS lines exhibited significant differences in all measured floral traits (days to heading (DTH), total stigma length (TSL), stigma width (SW), duration of spikelet opening (DSO), spikelet opening angle (SOA)). Additionally, L4 displayed the uppermost total stigma length and stigma width, whereas L1 and L5 recorded the best duration of spikelet opening and spikelet opening angle. Notably, these mentioned CMS lines exhibited the highest plant growth and yield traits, particularly under T4 treatment. Strong positive relationships were distinguished between the duration of the spikelet opening, panicle exertion, panicle weight, seed set, grain yield, total stigma length, spikelet opening angle, stigma width, and number of fertile panicles per hill. Cyanobacteria is a potential promising tool to increase floral traits and seed production in hybrid rice.
Water shortage stress is the most critical abiotic factor reducing rice yield. Water deficit stress at whichever of the rice critical growth stage causes decline in yield. A field experiment was conducted at the Experimental Farm of Sakha Agricultural Research Station, Kafrelsheikh, Egypt during 2018 and 2019 seasons, to investigate the effect of four irrigation intervals (continuous flooding(I1), irrigation every six days(I2), nine days(I3) and twelve days(I4)) on performance of five genotypes (Giza 178, IR 69625A/Giza 178, IR 70368A/Giza 178, IR 69625A/Giza 179 and IR 69625A/Giza 181). Strip plot design, with four replications was used. The horizontal plots were assigned to irrigation treatments, while the vertical plots were assigned to rice genotypes. Different drought tolerance indices such as abiotic tolerance index (ATI), stress susceptibility index (SSI), mean productivity (MP), tolerance index (TOL) and stress susceptibility percentage index (SSPI) were tested in screening superior rice genotypes. The results showed that days to 50% heading, plant height, panicle length, panicle weight, number of effective tillers hill-1 , spikelet's number panicle-1 , number of branches panicle-1 , seed set (%), 1000-grain weight (g), number of filled grains panical-1 , grain yield t ha-1 , harvest index (%) and biomass weight t ha-1 were highly significantly affected by the interaction between irrigation intervals and genotypes. The highest values of grain yield were obtained by IR69625A/Giza 181 under continuous flooding irrigation during both seasons. Based on results of different drought tolerance indices, IR69625A/Giza 181 showed lowest values of ATI, SSI and TOL and the highest values of MP and SSPI and was identified as drought tolerant genotype.
A field trial was performed in Randomized Complete Block Design (RCBD) with three replications at the Experimental Farm of Sakha Agricultural Research Station, Kafr ELSheikh, Egypt, during 2018 and 2019 rice growing seasons, to investigate the effect of three sowing dates (May 10 th , June 1 st and June 20 th) and four levels of nitrogen fertilizer (0, 55, 110 and 165 kg N/ha) on the productivity of Sakha Super 300 variety. The results showed that the sowing date June 1 st produced the highest grain yield 10.67 and 10.71 t ha-1 in both seasons. Nitrogen level of 165 kg N ha-1 produced the highest grain yield 10.50 and 10.45 t ha-1 without any significant difference with level of 110 kg N ha-1 in 2018 and 2019 seasons. The interaction between sowing dates and nitrogen levels was highly significant for number of panicles hill-1 , panicle length, number of filled grains panicle-1 , unfilled grains percentage and 1000-grain weight, as well as grain and straw yield and harvest index in both seasons. Interaction results showed that, the first sowing date (May 10 th) with nitrogen level of 110 kg N ha-1 gave the highest grain yield 10.91 and 10.79 t ha-1. On the other hand the second sowing date (June 1 st) with nitrogen level of 165 kg N ha-1 gave the highest grain yield 12.03 and 11.92 t ha-1 in 2018 and 2019 seasons. The highest values of accumulated growing degree days (GDD) and photo thermal units (PTU) were recorded when plants sown on May 10 th. On the other hand the maximums heat use efficiency (HUE) was achieved when Sakha Super 300 sown on 1 st June with application of 165 Kg N ha-1 in both seasons.
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