Improving crop varieties

Why we must raise yields

India has more than a billion people, and every one of them needs food every day. Most of that food comes from crops. The land that can be farmed is limited, and towns, roads and factories take some of it. So we cannot meet the need by ploughing more and more land.

We must grow more food on the same land. That means raising the yield, the amount of grain or other produce harvested from each hectare. A hectare is a square of land $100$ m on each side.

In the 1960s, India raised its grain production sharply. Better varieties of wheat and rice, more irrigation and more fertiliser all played a part. This is called the Green Revolution. It showed that careful farming can raise yields a great deal.

Kharif and rabi crops

India has two main crop seasons.

• Kharif crops are sown with the coming of the rains, in June, and harvested in October. Paddy, soyabean, pigeon pea, maize, cotton, green gram and black gram are kharif crops.
• Rabi crops grow in the cool winter, from November to April. Wheat, gram, peas, mustard and linseed are rabi crops.

Better varieties

A variety is a kind of crop with its own set of traits. Growing a better variety is the first way to raise the yield. How do breeders make one?

Hybridisation

In hybridisation, a breeder crosses two plants that differ in their traits. The offspring is a hybrid. The breeder picks the parents so that the hybrid may combine the good traits of both. For example, one parent gives a high yield and the other gives resistance to a disease. The breeder then selects the best offspring and grows it again.

The kind of hybridisation depends on the parents.

• Intervarietal: the parents are two different varieties of the same crop.
• Interspecific: the parents are two different species of the same genus.
• Intergeneric: the parents belong to two different genera.

Genetic modification

Another way is to put into the crop plant a gene that gives a useful trait, such as resistance to a pest. The gene may come from a very different living thing. A crop grown from such a plant is genetically modified.

What breeders aim for

A new variety is made with one or more of these aims.

• Higher yield. The variety gives more produce from each hectare.
• Better quality. What counts as quality differs from crop to crop: the baking quality of wheat, the protein quality of pulses, the oil quality of oilseeds and the keeping quality of fruits and vegetables.
• Resistance. Resistance to biotic stress means resistance to diseases, insects and nematodes. Resistance to abiotic stress means resistance to drought, salty soil, waterlogging, heat, cold and frost. A resistant variety loses less of the crop.
• A shorter time to ripen. If a crop ripens sooner, a farmer can grow more crops in a year, and each crop costs less to grow. A crop that ripens all together can be harvested in one go.
• Wider adaptability. The variety does well in different conditions, so one variety can be grown in many regions and seasons.
• A useful plant shape. Tallness and many branches are good in a fodder crop, since animals eat the whole plant. Dwarf plants are wanted in cereals, so that the plant uses fewer nutrients in growing tall.

What a better variety gives

Try the numbers below. Change the size of the field, the old yield and the extra that the new variety gives. See how the extra grain grows.

Try it in Python

The program works out the grain and the extra income from a new variety of rice on a farm.

Practise with new numbers

Common mistakes

• "A hybrid is the same as a genetically modified plant." A hybrid comes from crossing two parent plants. A genetically modified plant has a gene put in from outside.
• "Intervarietal and interspecific crosses are the same." An intervarietal cross is between two varieties of one crop. An interspecific cross is between two species of one genus.
• "The Green Revolution came from new seeds alone." Better seeds worked together with irrigation and fertiliser.
• "The variety with the highest yield is always the best." A variety also needs good quality and resistance, and it must suit the place where it grows.

Remember these

• Farmland is limited, so food production must rise by raising the yield from each hectare.
• Kharif crops are sown with the rains in June. Rabi crops grow in winter, from November to April.
• Hybridisation crosses two parents: intervarietal, interspecific or intergeneric. Genetic modification adds a gene.
• Breeders aim for higher yield, better quality, resistance, a shorter time to ripen, wider adaptability and a useful plant shape.
• Biotic stress is from living things such as pests. Abiotic stress is from drought, salt, heat and the like.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Why can India not feed its people just by farming more and more land?

2. Rice is sown in June with the coming of the rains. Is it a kharif crop or a rabi crop?

3. A breeder crosses two different varieties of mustard. What kind of hybridisation is this?

4. Name two kinds of abiotic stress that a variety may be bred to resist.

5. Why do farmers like a variety that ripens sooner?