Agriculture Reference
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confronted during transfer of resistance, various heat resistant inbred lines
and hybrid varieties with commercial acceptability have been developed
and released in different vegetables, particularly in tomato (Scott et al.,
1986, 1995).
AVRDC, Taiwan, has made significant contributions to the develop-
ment of heat-tolerant tomato and Chinese cabbage lines ( Brassica rapa
subsp. Pekinensis and chinenesis ) adapted to hot and humid climate. The
key to achieving high yields with heat-tolerant cultivars is the broadening
of their genetic base through crosses between heat-tolerant tropical lines
and disease-resistant temperate or winter varieties (Opena and Lo, 1981).
The heat-tolerant tomato lines were developed using heat-tolerant breed-
ing lines and landraces from the Philippines (viz., VC11-3-1-8, VC 11-
2-5, Divisoria-2) and the United States (viz., Tamu Chico III, PI289309)
(Opena et al. , 1992). However, lower yields in the heat-tolerant lines are
still a concern.
More heat-tolerant varieties are required to meet the needs of a chang-
ing climate, and these must be able to match the yields of conventional,
nonheat tolerant varieties under nonstress conditions. A wider range of
genotypic variation must be explored to identify the additional sources of
heat tolerance. For example AVRDC's tomato breeding line, CL5915, has
demonstrated high levels of heat ranges from 15% to 30%, while there
is complete absence of fruit set in heat-sensitive lines in mean field tem-
peratures of 35 °C. Now, new breeding lines have been developed from
CL5915 and other sources that exhibit increased heat tolerance. A CL5915
line is considered best combiners for percentage fruit set and total yield
in hybrids developed for heat-tolerance (Metwally et al. , 1996). Simi-
larly, EC-520061 ( Solanumhabrochaites ) can set fruits under both high
(40±2°C) and low (10±2°C) temperatures. Some heat tolerant breeding
lines of tomato likeCLN-2413R, CLN 2116B and COML CR-7 have also
been reported by Akhtar et al. (2012).
The Division of Vegetable Science, Indian Agricultural Research Insti-
tute, New Delhi has developed some varieties of vegetables to mitigate the
harmful effect of heat. Tomato varieties Pusa Sadabahar and one hybrid
Pusa Hybrid-1 have been developed which are tolerant to high tempera-
tures. Radish variety, Pusa Chetaki has been developed having better root
formation under high temperature regime, that is, April-August. Similarly
carrot variety, Pusa Vrishti can form root at high temperature and high
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