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ICRISAT develops hybrid pigeonpea with much higher yields

Dr KB Saxena is a pigeonpea expert with ICRISAT. He earned his PhD in plant breeding and genetics from GB Pant University of Agriculture and Technology, Pantnagar, India. He has been with ICRISAT since 1974. He has played an instrumental role in the recent development of the first commercial hybrid legume — a hybrid pigeonpea — which produces 30 per cent higher yields. In addition, he is actively promoting the use of pigeonpea for soil conservation in China and India and has already begun pilot projects on the same. He has over 200 publications to his credit.

In this interview by Matt McHugh, Dr Saxena talks about his achievement, which took over three decades to come to fruition and the current state of research in pigeonpea

What is the significance of the new development?
Botanically, pigeonpea is a perennial legume, but it is cultivated as an annual. It's a very hardy and multipurpose plant, used not only for grain, but also for other purposes such as fodder and efficient fuel wood.

Pigeonpea is very important for the rejuvenation of poor soil. It has a very deep root system — the root goes down five or six feet, so it can break all the hardpan inside the soil. Somehow, the roots will find a way to grow. And pigeonpea fixes 40–50kg atmospheric N / ha.

Also, there's phosphorus in the soil that is bound to the soil and not available to plants. The roots of pigeonpea produce an acid that breaks these bonds and make the phosphorus available to plants. In some places, such as Fiji, pigeonpea is used mainly with the goal of recycling nutrients. In Fiji, the main crop is sugarcane and pigeonpea is grown to replenish the soil.

Pigeonpea is very important as a sustainability crop. It doesn't require a lot of fertiliser or a lot of water to grow, so it's a poor man's crop in that sense. It can grow very well with less than 600–700 mm of water.

Traditional pigeonpea varieties are all long-duration types; they mature in about 300 days. They have very specific uses, and sometimes you'll find them growing as a perennial plant around houses, fencing, etc. As a perennial, it can survive 3–4 years easily. And the plant is also grown as a perennial if it's the long-poded type grown as a vegetable.

When we started the program at ICRISAT in '74, our prime objective was to reduce maturity so we could diversify cropping systems. So we started breeding early-maturing types. We now have very early varieties which can mature as early as 75–80 days.

Between those that mature at 75 days and those that mature at 300 days, if you look at the germplasm, you will find almost continuous variation that gives a breeder a lot of flexibility.

From the farmer’s perspective, which is the better choice - shorter duration or longer duration type? Are the yields different?
What happens is that, you don't grow many plants per unit area with the longer-duration plants, so per unit area, the yield is not much different. Pigeonpea is grown as an intercrop in most places, and the traditional varieties are always grown as intercrops. Intercrops give the benefit of yielding two crops per year. Pigeonpea initially grows very slowly. Later on, it grows more quickly. So, during the initial slow growth three-month period, another crop, such as soyabean (a three-month crop) can be grown. The soyabean–pigeonpea combination is the most beneficial one in central India.

Pigeonpea-to-pigeonpea rows will be around two metres, and in between, farmers put two rows of soyabean. Soyabean yields with intercropping are as good as those in regular cropping. The system has been developed in such a way as to give farmers something from that field even in very poor conditions — that's why it's called a sustainable crop.

This combination does very well, and we get a higher yield. Total profit per unit area is higher with this technique.

Once we developed the short-duration types, we developed the agronomic practices for them as well. We discovered that you have to grow these types in a high-density system, which is around 200,000 plants per hectare, compared to around 40,000 plants per hectare for normal types. Per unit area, dry-matter production is almost the same, because these are smaller plants.

But each has its own advantage and disadvantage.

Improving yield: A very unfortunate thing has happened in this crop — over the last 60 years, there has been no improvement in its yield. Area under pigeonpea cultivation has increased, because we've developed varieties that are resistant to diseases or are early maturing or better adapted to certain areas, but yield per se has not increased significantly.

Because of this, at ICRISAT, we decided we should go for some type of alternate breeding system, and that's where the idea of the hybrid originated.

Most pulse crops are 99 per cent self-pollinating, but pigeonpea is not. In pigeonpea, you get about 30 per cent outcrossing. So we exploited that. Once there is natural outcropping, seed production becomes easy. But our major problem was that we didn't have any male-sterile material. (This means that the male parts of the plant are inactive, therefore making the plant effectively only female and preventing self-pollination.)

Initially, we searched for a mutant with those characteristics, but we didn't succeed, so we started a deliberate programme to produce one. We crossed wild varieties of pigeonpea with domesticated varieties — the different species are from 60 to 80 per cent related.

The plan was to get cytoplasm from one plant, the nucleus from the other, and end up with a genome that has male sterility. We didn't succeed for quite some time — it took about 30 years to develop it. But we're very happy that something has finally come out of all this work. And it's a very stable system.

Now we're looking for hybrids that give about 30–40 per cent higher yield, because if you have to buy new seeds every year, the advantage has to be sufficient to justify this. In normal, non-hybrid varieties, farm-saved seeds can be used for three to four years before new seeds should be bought; some farmers go over a decade without buying new seeds. With hybrids, however, farm-saved seeds possess only about 25 per cent of the vigour of the hybrid parents, so yield quality is greatly reduced.

The hybrid seeds have already been released to some farmers — these farmers get the benefit of the new seeds in exchange for feedback on their experience with it, supplying ICRISAT with data that can be used to further improve the hybrid.

Last year, we conducted trials in around 800 of these on-farm demonstrations, and, on average, the hybrid was 28 per cent better than varieties.

In some fields, there was no advantage, while in others there was a 120 per cent advantage. But the mean additional yield was about 28 per cent, which we were quite happy with.

Taking technology to the farmer: Now that we have the developed a seed-production technology, the question is how to make sure the new technology reaches farmers. For that, we've made contact with private seed companies. We have a kind of consortium. We take money from the private companies to fund our research, and they get seeds for the parent plants that were used to create the hybrid — they then create their own hybrids and make money by selling those seeds. We also provide the same materials to universities and national programs.

One hybrid is already in farmers' fields in trials, and another hybrid is ready to go.

One variety should be released this year. It’s currently in pre-released condition, and has already been released as truthfully labelled seeds, where the producer (as opposed to the seed company) takes responsibility for the seed quality.

 
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