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Global warming has now arrived in the northeast | Thai farmers can feel the impact
Thung Kula Rong Hai, an area of 2.1 million rai spanning 5 northeastern provinces. The research institute of Khon Kaen University reported that global warming clearly affects growing Khao Dawk Mali rice, cutting the yield of Thai fragrant rice by as much as 45%. Farmers face alternating floods and droughts. The future of Khao Dawk Mali therefore lies in breeding it to tolerate drought, flooding and insects. In addition, higher temperatures obstruct pollination and make pollen sterile, which greatly reduces rice yield. Global warming severely affects rainfed paddies. Rainfed paddies are the vast paddy lands of Mekong basin countries from Myanmar to Vietnam, which must wait for rain alone for cultivation. Native rice varieties have adapted to limiting growth conditions, so these native varieties must be bred to be even more tolerant. A problem expected under global warming is that insects will adapt better and spread heavily. Can biotechnology be the answer? Read on in this article.
Khao Dawk Mali 105 Resistant to Brown Planthopper The brown planthopper (Nilaparvata lugens) is one of the important natural insect enemies that lowers rice yield in both rainfed and irrigated areas, with outbreaks in both the main season and off-season. Both nymphs and adults damage rice by sucking sap from the phloem and xylem cells at the base of the rice plant above the water surface, causing the plant's leaves to turn yellow and dry like being scalded with hot water, and dry up and die in patches, called hopperburn. Hopperburn is generally seen from the tillering stage to the heading stage, which matches the 2nd–3rd generations of the brown planthopper in rice fields. In fields lacking water, nymphs move down to the base of the hill or onto wet, moist ground. In addition, the brown planthopper is a vector of the viruses that cause rice ragged stunt and rice grassy stunt, making rice short, stunted and heading not at all or poorly with imperfect grains, lowering rice yield by as much as 90 percent.
Breeding Rice Resistant to Brown Planthopper Because brown planthopper outbreaks occur every year and in many areas of Thailand, breeding rice resistant to the brown planthopper is a highly important approach. Searching for rice lines with broad resistance to the brown planthopper, by testing various varieties and using insect populations of different biotypes, found that the lines PTB33 and Rathu Heenati resist every insect population collected. These two lines were then crossed with Khao Dawk Mali 105 (KDML105), a rice whose cooking and eating quality consumers like but which is not resistant to the brown planthopper. Selection was then done for the planthopper resistance gene region on chromosome 6 using DNA molecular markers together with planthopper resistance testing and backcrossing, until Khao Dawk Mali 105 and glutinous RD6 with resistance to the brown planthopper were obtained.
Khao Dawk Mali 105 Resistant to Blast Rice blast is caused by the fungus Pyricularia grisea which can attack rice plants from the seedling stage to harvest, with symptoms found on every aboveground part of the rice plant. It has been estimated that each year the yield of Khao Dawk Mali 105, a blast-susceptible variety, loses about 5–10 percent of the total yield to this disease. Even though rice has been bred to resist blast, soon after the new variety is promoted for planting, the pathogen develops itself to be able to attack that resistant variety. It is therefore necessary, and a great challenge, to breed rice with lasting resistance to blast.
Breeding Blast-Resistant Rice
Hom Nin non-glutinous rice and IR64 are varieties with high potential to resist the blast fungus in Thailand. The positions of blast resistance genes have been studied and molecular markers developed to help in rice breeding. Two breeding methods have been carried out: breeding rice by adding blast resistance to Khao Dawk Mali 105 through backcrossing, and stacking blast resistance genes from Hom Nin and IR64 together to give Khao Dawk Mali 105 with added blast resistance.
Breeding Khao Dawk Mali 105 for Drought Tolerance
Drought is an important problem in rainfed farming areas, especially rice-growing areas in the north and northeast, where every year there is usually uncertainty in the amount and distribution of rainfall, so drought and flooding occur regularly. This drought can occur at any growing stage, namely early, mid or late in the rainy season, and in a severe drought year both early and late in the planting season. Drought occurring while rice is heading greatly lowers yield, and in a severe drought year farmers may get no rice yield at all.
The goal of breeding Khao Dawk Mali 105 for drought tolerance therefore focuses on taking QTLs from drought-tolerant varieties related to raising yield potential, drought escape through flowering 1–2 weeks earlier, tolerance of water deficit through physiological mechanisms, and a deep root system, and putting them into Khao Dawk Mali 105 using marker-assisted selection (MAS).
Experimental results
Testing the improved Khao Dawk Mali 105 lines carrying drought-tolerant donor segments on chromosomes 1, 3, 4 and 8, under drought severe enough to lower yield by 50%, found better growth, reduced percent sterility, and high grain weight accumulation. Although breeding with MAS has shown a degree of success, in the later stages of selection it is necessary to select for drought tolerance traits and yield under drought in experimental plots, and plants showing good traits under drought arise from combining the good QTLs of the drought-tolerant variety and Khao Dawk Mali 105.
