The Hindu Business Line : Broomrape weed threatens mustard crop

"In mustard, we are seeing it for the first time in this form. Having diagnosed it only now, it will take us some time to come out with an appropriate solution."

Jhunjhunu (Rajasthan) , Feb. 16

EVEN as the country is set to harvest a bumper rabi mustard crop of around six million tonnes (mt) this year, farmers here are a worried lot over the infestation of a new weed, Orobanche ramosa or broomrape. Scientists fear the weed could, over a period of time, play havoc with the crop "similar to what Phalaris minor has done for wheat".

"This weed used to appear in a few small patches in the last 2-3 years. But this time, we are seeing it on a big scale," said Mr Dayanand, a farmer from village Bhaisawata Khurd, whose entire 26 bigha (around 6 acres) plot has been infested. As of now, the weed has been reported mainly in the Shekhawati region of Rajasthan (Jhunjhunu, Churu and Sikar districts), besides in isolated pockets of Nagaor and Alwar. Rajasthan accounts for about 40 per cent of the country's total rapeseed-mustard output.

"The problem is not widespread today. But in the coming years, it could well emerge as a major threat for the mustard crop," Dr S. Nagarajan, Director of the New Delhi-based Indian Agricultural Research Institute (IARI), warned. Broomrape is basically an annual root parasitical herb, consisting of a 10-15 inch fleshy stem, pale yellow or brownish-red in colour and bearing white, tubular flowers.

Mustard is normally sown in mid-October. The broomrape seeds germinate about 40 days later, when the mustard roots have been fully established. In fact, it is the chemical exudates of the mustard roots that induce germination of the broomrape seeds within the soil. The seedlings subsequently infect the host root. "Since the weed is totally devoid of chlorophyll, rendering it incapable of producing its own food through photosynthesis, it penetrates into the roots of the host and draws nourishment from there," Dr Nagarajan stated.

As a result, the mustard ends up `competing' with the weed for nutrients and water, translating into yield losses of 25-30 per cent. "We usually get 1.3-1.4 tonnes of mustard per hectare in these parts. This time, it could fall to one tonne," said Mr Navrang Singh, a former MLA from Nawalgarh constituency in Jhunjhunu.

Worse, each broomrape plant produces over 5 lakh seeds (against 1,000-odd for mustard) that are shed around 10 days before the mustard crop is harvested by early-March. "Being very small and light, they can be disseminated by wind or birds. Even in the soil, they can remain dormant for up to 10-12 years," Dr R.S. Malik, Principal Scientist (Mustard), IARI, said.

Significantly, State Agricultural Department officials could not even diagnose the weed when it was reported to them by distressed farmers. "We were told about it last month by an IARI aluminus, Dr Mahender Singh Somra, who belongs to that area. It was he who took the whole trouble of collecting the samples of the weed and bringing it to us for diagnosis," Dr Nagarajan said.

Incidentally, broomrape is a known root parasite in tobacco, tomato, brinjal and other Solanaceous plants. "But in mustard, we are seeing it for the first time in this form. And having diagnosed it only now, it will take us some time to come out with an appropriate solution," he said, while expressing doubts over the effectiveness of conventional broad-spectrum weedicides.

One way out, scientists say, would be varietal change. "Most farmers here are growing for the last many years T-59, a mustard variety that could be particularly susceptible, just as WL-711 wheat was to Phalaris minor. Replacement of varieties could possibly help, as it has in the case of Phalaris minor," Dr Nagarajan said. But this, he admitted, was only a hypothesis.

The other solution being advocated is to get farmers to thoroughly plough the soil in March-April, after the wheat or mustard is harvested. "The bulk of the weed seeds are found in the top 1.5 inch depth of the soil. Ploughing, along with the dry heat exposure during April, will destroy and considerably reduce the viability of the seeds," Dr Nagarajan added.

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