SYNTHETICS VARIETIES

 

SYNTHETICS  VARIETIES

 

 The possibility of commercial utilization of synthetic varieties in maize was first suggested by Hayes and Garber in 1919. synthetic varieties have been of great value in the breeding for those cross-pollinated crops where pollination control is difficult, e.g., forage crop species, many clonal crops like cacao, alfalfa (M.Sativa), clovers (Trifoulim sp.) etc. The maize improvement programme in India now places a considerable emphasis on synthetic varieties. The maize programme of CIMMYT. Mexico, is based on population improvement; the end-product of such a programme is usually a synthetic variety.

 

DEFINITIONS

A synthetic variety is produced by crossing in all combinations a number of lines that combine well with each other. Once synthesized, a synthetic is maintained by openpollination in isolation. Some breeders use the terms synthetic variety in a restricted sense : a 104 synthetic variety is regularly reconstructed from the parental lines and is not maintained by open-pollination.

 

OPERATIONS IN PRODUCING A SYNTHETIC VARIETY

 

By definition, a synthetic variety consists of all possible crosses among a number of lines that combine well with each other. The lines that make up a synthetic variety may be inbred lines, clones, open-pollinated varieties, short-term inbred lines or other populations tested for GCA or for combining ability with each other. The operations involved in the production of synthetic varieties are briefly described below.

 

Production of A Synthetic variety

A synthetic variety may be produced in one of the following two ways

1. Equal amounts of seeds from the parental lines are mixed and planted in isolation. Open-pollination is allowed and is expected to produce crosses in all combinations. 105 The seed from this population is harvested in bulk; the population raised from this seed is the Syn1 generation.

 2. All possible crosses among the selected lines are made in isolation. Equal amounts of seed from each cross is composited to produce the synthetic variety. The population derived from this composited seed is known as the syn1 generation.

 

Multiplication of Synthetic Varieties

 After a synthetic variety has been synthesized, it is generally multiplied in isolation for one or more generations before its distribution for cultivation. This is done to produce commercial quantities of seed, and is a common practice in most of the crops, e.g., grasses, clovers, maize etc. But in some crops, e.g., sugarbeets, the synthetic varieties are distributed without seed increase, i.e., in the Syn1 generation

 

MERITS OF SYNTHETIC VARIETIES

 Synthetic varieties offer several unique advantages in comparison to hybrid varieties in the exploitation of heterosis. These advantages are listed below.

 

 

1. Synthetic varieties offer a feasible means of utilizing heterosis in crop species where pollination control is difficult. In such species, the production of hybrid varieties would not be commercially viable.

2. The farmer can use the grain produced from a synthetic variety as seed to raise the next crop.

3. In variable environments, synthetics are likely to do better than hybrid varieties. This expectation is based on the wider genetic base of synthetic varieties in comparison to that of hybrid varieties.

4. The cost of seed in the case of synthetic varieties is relatively lower than that of hybrid varieties.

5. Seed production of hybrid varieties is a more skilled operation than that of synthetic varieties.

 

DEMERITS OF SYNTHETIC VARIETIES

 1. The performance of synthetic varieties is usually lower than that of the single or double cross hybrids. This is because synthetics exploit only GCA, while the hybrid varieties exploit both GCA and SCA.

2. The performance of synthetics is adversely affected by lines with relatively poorer GCA. Such lines often have to be included to increase the number of parental lines making up the synthetic as lines with outstanding GCA are limited in number.

 3. Synthetics can be produced and maintained only in cross-pollinated crop species, while hybrid varieties can be produced both in self- and cross-pollinated crops.

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