Fig. 22.1. Schematic presentation of transfer of Xa-21 from original source to cultivated rice by conventional and molecular breeding. From Datta, 1998.5
PR genes in intra- and extracellular tissue provides enhanced fungal resistance, which allows a reduced application of fungicides. We have introduced a PR-5 gene, D34 (thaumatin-like protein gene), in rice, which showed enhanced resistance to sheath blight (Fig. 22.2b).11 We are now aiming to develop transgenic rice with multiple genes, and assume that this is a better strategy for durable resistance because of gene pyramiding (Table 22.5).
Transgenic Rice With Xa-21 Conferring Resistance To Bacterial Blight
Bacterial blight (BB) caused by Xantho-monas oryzae pv. oryzae (Xoo) is one of the most destructive diseases of rice throughout the world. A schematic presentation compares conventional breeding and the relative advantage of molecular breeding with Xa-21 (Figs. 22.1 and 22.2c). However, durable resistance can be achieved only with gene pyramiding, as was done in transgenic IR72. This is a very efficient way to improve BB resistance in a desirable cultivar without the negative impact of genetic linkage dragging.
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