Seed Production

Introduction

Production of high quality seed requires considerable technical skill and a number of rigid requirements must be fulfilled in order to ensure a high purity and germination of seed. Seed multiplication involves two aspects, seed production and Seed processing.

Seed production requires improved cultural practices, efficient weed, disease and pest control, optimum irrigation and fertilizer inputs and some other specific operations.

Seed production

Seed production for convenience, may be dealt with in two subheads: Isolation, and Cultivation.

Isolation

The crop raised for seed production should be separated from other fields of the same crop species by a minimum distance, which varies from one crop to the other. This distance is known as isolation distance. Isolation is essential to prevent pollination from unwanted pollen in the case of cross-pollinated and often cross-pollinated species and to avoid mechanical mixture and chance of cross-pollination in self-pollinated species. The isolation distance varies from 3 m in self-pollinated crops like wheat, rice, etc. to 200 m in the case of maize, bajra and jowar to even 400 m in case of jowar when the isolation is from Johnson grass (Sorghum halepense). In some cases, e.g., hybrid maize the minimum isolation distance may be considerably reduced by planting border rows of the pollinator parent and by choosing a larger field for seed production. The minimum isolation distance required for a foundation seed crop is markedly greater than that for a certified seed crop in the case of all those crops where pollen contamination is feared.

Minimum Isolation distance of different crops for seed production

Cultivation

Land requirement

The land should be level, fertile and free from noxious weeds common to the crop. In some cases, like bajra and jowar, the field to be used for seed production should not have been used for growing the same crop in the previous year. If the same crop was grown in the previous year, the field should be irrigated 3 weeks before sowing and ploughed just before sowing. This is done to allow the seeds that might have dropped in the field from the previous crop to germinate, and to destroy the seedlings by ploughing.

Cultural practices

Recommended improved cultural practices must be followed for raising a good seed crop. Recommended dose of fertilizers and irrigation water must be applied for high yields of high quality seed. Poor cultural practices would give lower yields and seeds of smaller size which would be rejected at the time of grading. This would drastically reduce the profits of seed growers.

Plant protection

Adequate measures must be taken to protect the seed crop from disease and pests. Insect pests and diseases may cause considerable damage to the crop reducing the yield and quality of seed. Further, incidence of some disease may lead to rejection of the seed by the certifying agency as unfit for use as seed. For e.g., the maximum permitted incidence of head smut and grain smut in jowar (S.bicolor, seed parent only) is one head in 10,000 and one head in 2,500 respectively, at the time of last held inspection. This rigid requirement with respect to disease is prescribed to prevent the occurrence of disease epidemics due to contaminated seed.

Weed control

Effective weed control is a must for good seed production. Weeds reduce crop yields and weed seeds contaminate the seed. Certain weeds are classified as objectionable weeds by the seed certification agency and the seed field is generally required to be free from such weeds. For e.g., in case of hybrid bajra, no objectionable weeds should be present at any field inspection, if they are present, the seed field may be rejected.

Rouging

Rouging is the removal of plants which are off type, that is, phenotypically different from the plants of the variety under certification. It is an important aspect of seed production and is necessary to prevent outcrossing and mechanical mixture. The off-type plants are regularly removed from the field either by uprooting or by cutting at the ground level. The off-type plants may differ in plant height leaf characters, flowering time, maturity etc.

Special operations

Seed production in certain crops may require some special operations. For e.g., hybrid maize seed production requires detasseling of the female parent before they shed pollen. Further, in hybrid seed production, the rows of male parent are harvested before the rows of female parent to avoid mechanical mixture of the two.

Harvesting

Harvesting and threshing of a seed crop should be done with considerable care in order to prevent mechanical mixture from other crop seed or weed seeds. The threshing floor should be clean and preferably cemented to keep the contamination by inert matter to a minimum. Care should be taken during threshing so as to avoid damage to seeds.