A large-scale backcross breeding pr

A large-scale backcross breeding project has been undertaken to improve drought tolerance in rice. Over 160 donor cultivars from 25
countries have been used in this project, representing a significant proportion of the genetic variation in cultivated rice. These cultivars were
evaluated in field experiments in the Philippines to assess their responses to drought in terms of plant height, heading date, and grain yield.
Drought was imposed near heading stage, in experiments that were established either in lowland (anaerobic) fields or upland (aerobic) soil.
Despite the poor adaptation of some cultivars to the tropics, it was possible to identify significant variation in plant response to drought
treatments, and contrasting effects on flowering delay and growth. Subsequently, 325 BC
2
F
2
bulk populations, developed by backcrossing
many of these donors to one of three elite recurrent parents, were screened under drought in lowland or upland nurseries. Stress levels were
managed to eliminate almost all seed set in recurrent parents, and those progeny that produced grain were selected as being putatively drought-
tolerant. The selection intensity varied across years and in selection environments with more severe stress, higher selection intensity could be
imposed. The number of plants selected within a population was not associated with the per se drought response of the donors in the direct
evaluation, indicating the wide presence of cryptic genetic variation for drought tolerance in the apparently drought-susceptible cultivars. The
genetic background of the recurrent parent affected the number of plants selected, as did the selection environment (upland versus lowland
nurseries). These drought-selected introgression lines represent a useful genetic resource to develop improved cultivars for farmers in rainfed
or water-scarce rice-growing regions, and also to improve our understanding of the genetic and molecular basis of drought tolerance in rice.
Genetic analysis of the selected lines, reported elsewhere, indicated specific regions of high introgression. Yield evaluations of the selected
lines are now underway across a range of drought scenarios.
#
2005 Elsevier B.V. All rights reserved

ผลลัพธ์ (อังกฤษ) 3:

A large-scale backcross breeding project has been undertaken to improve drought tolerance in rice. Over 160 donor cultivars from 25 countries have been
used in this project, representing a significant proportion of the genetic variation in cultivated rice. These
cultivars were evaluated in field experiments in the Philippines to assess their responses to drought in terms of plant height,heading date, and grain yield.
Drought was imposed near heading stage, in experiments that were established either in lowland (anaerobic) or upland fields (aerobic) soil.
Despite the poor adaptation of some cultivars to the tropics, it was possible to identify significant variation in plant response to drought
treatments, and contrasting effects on growth and flowering delay. Subsequently,325 BC F

2
2
bulk populations, developed by backcrossing
many of these donors to one of three Elite recurrent parents, were screened under drought in lowland or upland nurseries. Stress
levels were managed to eliminate almost all seed set in recurrent parents, and those that produced grain progeny were selected as being putatively drought-tolerant
.The selection intensity varied across years and selection in environments with more severe stress, higher selection intensity
could be imposed. The selected number of plants within a population per se was not associated with the drought response of the donors in the
direct evaluation,Wide indicating the presence of cryptic genetic variation for drought tolerance in the apparently drought-susceptible cultivars. The
genetic background of the recurrent parent affected the number of selected plants, as did the selection environment (versus upland lowland
nurseries).These drought-selected genetic introgression lines represent a useful resource to develop improved cultivars for farmers in rainfed
or water-scarce rice-growing regions, and also to improve our understanding of the genetic and molecular basis of drought tolerance in rice. Genetic
analysis of the selected lines, reported elsewhere, indicated specific regions of high introgression.
Yield evaluations of the selected lines are now underway across a range of drought scenarios.

2005 # Elsevier B.V.All rights reserved