Elementary plant Biochemistry and Biotechnology (2+1)

Ovary culture

• Culture of unfertilized ovaries to obtain haploid plants from egg cell or other haploid cells of the embryo sac is called ovary culture and this process is termed as gynogenesis. San Noem first reported the gynogenesis in barley in 1976. Subsequently, success has been obtained in several species including wheat, rice, maize, tobacco, sugar beet, rubber etc. About 0.2-6% of the cultured ovaries show gynogenesis and one or two, rarely up to 8, plantlets originate from each ovary. The rate of success varies considerably with species and is markedly influenced by the genotype so that some cultivars do not respond at all. E.g. In rice, japonica genotypes are far more responsive than indica genotypes.


• In most cases, the optimum stage for ovary culture is the nearly mature embryo sac, but in rice ovaries at free nuclear embryo sac stage are the most responsive. Generally, culture of whole flowers, ovary and ovules attached to placenta respond better, but in Gerbera and Sunflower isolated ovules show better response. Cold pretreatment (24-48 hr at 4⁰C in sunflower and 24 hr at 7⁰C in rice) of the inflorescence before ovary culture enhances gynogenesis.


• Growth regulators are crucial in gynogenesis and at higher levels they may induce callusing of somatic tissues and even suppress gynogenesis. Growth regulator and sucrose requirement seems to depend on species. Ovaries are generally cultured in light, but at least in some species, e.g. sunflower and rice, dark incubation favours gynogenesis and minimizes somatic callusing; in rice light may lead to degeneration of gynogenic proembryos.


• Generally, gynogenesis has two or many stages and each stage has distinct requirements. In rice, tow stages viz., induction and regeneration, are recognized. During induction, ovaries are floated on a liquid medium having low auxin and kept in dark, while for regeneration they are transferred on to an agar medium with higher auxin concentration and incubated in light. As in anther culture, gynogenesis may occur either via embryogenesis or through plantlet regeneration from callus. In general, regeneration from a callus phase appears to be easier than direct embryogenesis.

Advantages

1. Gynogenetic haploids may be a valuable substitute for the production of homozygous lines in cases where cytoplasmic male sterility prevents the use of micropsores.
2. Reduction in the frequency of albino plants in some species especially cereals.
Limitations:

1. So far it has been successful only in less than two dozens species.
2. The frequency of responding ovaries (1-5%) and the number of plantslets/ovary (1-2) I quite low. Therefore, anther culture is preferred over ovary culture. Only in those cases where anther culture fails, e.g. sugarbeet and for male sterile lines, ovary culture assumes significance.