Cereals processing technology

Rice production 95
Rice disease resistance gene, Xa21
The rice Xa21 gene, which confers resistance to Xanthomonas oryzae pv. oryzae
race 6, was isolated by positional cloning. 27 Fifty transgenic rice plants carrying
the cloned Xa21 gene display high levels of resistance to the pathogen. The
sequence of the predicted protein, which carries both a leucine-rich repeat motif
and a serine-threonine kinase-like domain, suggests a role in cell surface
recognition of a pathogen ligand and subsequent activation of an intracellular
defense response. Characterization of Xa21 should facilitate understanding of
plant disease resistance and lead to engineered resistance in rice.
Fertile transgenic rice
Shimamoto et al. 28 reported on fertile transgenic rice plants regenerated from
transformed protoplasts. Redona and Mackell 26 made a quantitative trait locus
analysis for rice panicle and grain characteristics. The development of molecular
genetic maps has accelerated the identification and mapping of genomic regions
controlling quantitative characters referred to as quantitative loci or ATLs. 15
Submergence tolerance genome mapping on rice chromosome 9
A major locus for submergence tolerance mapped on rice chromosome 9 has
been reported by Xu and Mackill. 34 Submergence stress is a widespread problem
in rice-growing environments where drainage is impeded. The authors used
RAPD (random-amplified polymorphic DNA) and restriction fragment length
polymorphism (RFLP) markers to map submergence tolerance in 169 F2 plants
and the resulting F3 families of a cross between a tolerant indica rice line, IR
40931-26 and a susceptible japonica line, P 1543851. IR 40931-26 inherited
strong submergence tolerance from the unimproved cultivar FR 13A. Eight day
old F3 seedlings were submerged for 14–16 days in 55 cm deep tanks, and
tolerance was scored after seven days recovery on a scale of 1 (tolerant) to 9
(susceptible). The tolerant and susceptible parents scored 1.5 and 8.4
respectively, and the F3 means ranged from 1.6–8.9. Two bulks were formed
with DNA from F2 plants corresponding to the nine most tolerant and the nine
most susceptible F3 families. Of 624 RAPD primers used to screen the bulks,
five produced bands associated with either tolerance or susceptibility. The
markers were mapped to a region of chromosome 9 by linkage to RFLP markers.
A submergence tolerance quantitative trait locus (QTL), here designated Sub l.
was located ca. 4 cm from the RFLP marker and accounted for 69% of the
phenotypic variance for the trait.
Genetic variation for traits related to temperate adaption of rice cultivars
MacKill and Lei 20 reported on genetic variation for traits related to temperate
adaption of rice cultivars. Rice (Oryza sativa L.) was cultivated in diverse
environments including temperate, subtropical, and tropical regions. Temperate
rice areas are dominated by the japonica subspecies, while indica cultivars are
confined.