| Two-line technique using photothermosensitive genie male sterile (PTGMS) indica rice as the male sterile line and maintainer line is an important tool in advancing hybrid rice technology. However, with the increasing level of susceptibility of the widely used restorer line 'Minghui 63' to bacterial blight (BB) in China (Chen et al. 2000), there is an urgent need to select new PTGMS lines that confer resistance to most known races of Xoo. The response of photothermosensitive genie male sterility in indica rice carrying Xa21 gene for RBB resistance was evaluated under field conditions using six PTGMS lines. The materials used in this study included Pei'ai64S as a control and five new PTGMS lines Viz: Gl. G2, G3. G4. and G5. The response to varying temperature conditions in nature of the lines was discussed and fertility stability of the lines was evaluated by AMMI model using fertile pollen (%), and also inoculating with Xoo race 4 to identify and select for resistance were analyzed.All analysis concentrated on the use of temperature factor as a determinant rather than daylength, and the predominant role of temperature in inducing fertility transformation in these lines under natural condition was ascertained. Under conditions of high temperature >25癈 the selected PTGMS lines were all completely sterile, but the reverse was the case under the low temperature (<25癈). All the PTGMS lines had a sterility period from lsl August to mid-September, and the new PTGMS lines had no pollen for a considerable period of time at the sterile stage before they entered the phase of pollen fertility in the month of September. The critical sterility point (CSP) of Pei'ai64S was 25.TC and it was higher than the new PTGMS line G3 (24.1癈). It was observed that the selected PTGMS lines had two distinct sensitive periods of fertility alteration: sterility period and transformation period, with a brief intermediary period between the two sensitive periods during the year 2001. The sterility period of new PTGMS lines varied from 23-43 days, which was longer for G2 due to its early heading date. Traits like duration, initial date and 15-day thermosensitive temperature for male sterility, and the initial date and 15-day thermosensitive temperature for optimum fertility were all correlated. Highly negative correlation with temperature and the high CSP observed in these lines suggested that these lines are highly responsive totemperature; most likely the predominant role maximum temperature and they might as well belong to the type thermosensitive genie male sterility (TGMS).Pei'ai64S was highly sensitive to temperature, much more than the new PTGMS lines. The results from analysis by the AMMI model showed that the interaction of genotype, sowing stages and genotype x sowing stages of PTGMS lines were highly significant by F-test. It clearly revealed that El, E2 and E3 environments were the most important stages for sterility, but the geographical condition was not varied enough to thoroughly investigate the fertility stability of these lines through the AMMI model.The study also revealed that the spikelets opening time varied only slightly from one genotype to the other and the time interval between 10:00am and 14:00pm had the highest spikelet opening rate for all the lines. The total number of flowering per day was highest in Pei'ai64S followed by Gl line. The new PTGMS lines (G2, G3, and G5) had an extended flowering time till 4:00h just likePei'ai64S.The new PTGMS lines G2 and G3 showed resistance to RBB, and they were confirmed to be having the Xa21 gene for resistance to RBB. This further led to the selection of the new PTGMS line G3 because of its closely related sterility expression with Pei'ai64S and its added advantage to confer resistance to RBB.
|
PDF Full Text Request