October 27, 2016 3:41:26 am
Hot and dry weather raises the chances of whitefly attacks, as Punjab’s farmers discovered for cotton last year. This year, it is humid and warm conditions, particularly in September, that has put paid to their hopes of a bumper paddy harvest. The villain: an innocuous-looking insect called the brown plant hopper (BPH).
Unlike most other pests, this one typically strikes very late, when the paddy crop is already 80-90 days old and in the final grain-filling stage. The female moths lay eggs from early-September that hatch within 10 days. The larvae emerging from them are the real baddies. These immature nymphs settle at the lower stem or culm of the paddy plant, from where they start sucking the sap. Since this sap rich in carbohydrates is transported through the phloem tissues to the grains that are still forming, it being sucked also impacts filling.
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“The resultant grains tend to be ill-filled, light-weight and chaffy. While it may appear that the farmer has harvested 20-21 quintals of basmati paddy per acre, actual yields would be only 15-16 quintals. The farmer will also get a lower price because there would be a higher percentage of broken rice produced during milling,” explains A K Singh, head of the Indian Agricultural Research Institute’s (IARI) division of genetics.
The entire lifecycle of the BPH insect – from the laying of eggs to the larvae becoming adult moths – is just 25-30 days, of which the most dangerous nymphal stage lasts 15-20 days. “This time, the maximum nymphal population was noticed from September 25 at the grain-filling stage (when the milky starch material turns first into soft and then hard dough) about a week or 10 days before harvest. The sultry and cloudy weather was clearly favourable to the buildup,” notes Singh.
According to Sarjiwan Singh Manhas, research & development head of Syngenta South Asia, BPH infestation is often difficult to detect since the pest attacks the lower portions of the paddy stems. “We tell farmers to go for prophylactic insecticide spraying. It should be done when they notice even a few hoppers in neighbouring fields in the early stages of the crop. The usual practice, instead, is to spray when the build-up has already happened and the plant would have grown to some three feet height, at which the required quantum of the chemical may not reach the bottom parts where the insect is present,” he points out.
The Switzerland-based (now Chinese-owned) Syngenta’s product ‘Chess’ — the active ingredient molecule is pymetrozine — is seen as the most effective against BPH today. “In our 200 demonstration plots and two learning centres attended by 10,000 farmers in Punjab and Haryana, we have shown that you can control the pest through timely and the right kind of spraying. The paddy grown in these sites did not suffer yield loss even this year when infestation levels were so high,” claims Manhas.
Pritam Singh Hanjra, a progressive farmer from Urlana Khurd village in Haryana’s Panipat district, does not dispute the effectiveness of ‘Chess’, but is concerned about the price. “It costs Rs 6,000 per kg and you need to spray 120 grams per acre. That works out to Rs 720, excluding the cost of spraying itself which is another Rs 200 per litre. Also, I don’t know how long it will be effective. Earlier, we were using Applaud (buprofezin molecule of Dow Chemical), Actara (Syngenta’s thiamethoxam) and Confidor (Bayer’s imidacloprid), but the pest has developed resistance against all of these,” he says.
Moreover, it isn’t just BPH. Paddy farmers are also spraying against other pests such as stem borer and neck blast. “The most effective chemicals to control them now are Coragen (chlorantraniliprole) and Galileo (picoxystrobin) respectively, both belonging to DuPont. These again cost between Rs 700 to Rs 800 per acre each. As farmers, we have no choice but do everything to protect our crop,” complains Hanjra.
An alternative approach to spraying, which the IARI is presently working at, is to breed for resistance through introduction of genes sourced from both traditional landrace cultivars as well as wild relatives of paddy.
The country’s premier publicly-funded farm research institute has transferred the ‘Pi9’ gene obtained from Oryza minuta (a wild relative of normal cultivated rice, which is Oryza sativa) to its popular Pusa Basmati-1 variety, in order to make the latter “moderately resistant” to neck blast and “highly resistant” to leaf blast fungus. Likewise, two genes — ‘Xa21’ from Oryza longistaminata (another wild relative) and ‘xa13’ from BJ1 (a traditional landrace) — have been incorporated into Pusa Basmati-1 to confer resistance to the deadly bacterial blight pathogen.
For BPH control, too, IARI is looking at transferring the ‘Bph 17’ gene sourced from Rathu Heenati (a traditional Sri Lankan red rice cultivar) and the ‘Bph 18’ gene from Oryza australiensis (a wild relative) into its improved Pusa-1121 and Pusa Basmati-6 varieties.
“In all these cases, the transfer of the target genes from the resistant donor lines has been achieved through molecular breeding based on marker-assisted selection. We did this first in basmati varieties, because there is a huge export market for this rice and farmers cannot risk too much application of pesticides. Through molecular breeding, we are ensuring that only the particular genes of interest get introduced without compromising on the unique basmati grain traits,” informs A K Singh.
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