Rapeseed and mustard crops are the second most important source of edible oil after groundnut in India. The average yield of these crops is around 600 kg/ha which has been static for several years. These low yields are of increasing concern in view of the short supply of oil seeds in India. Considerable breeding efforts are being directed to improving production potential as well as stability of yield in these crops (Prakash, 1980). An understanding of the physiological basis of yield formation can be of great help in selecting for high and stable yields. However, there is little information available on the production physiology of these crops (Mehrotra, Saxena & Moosa, 1976; Bhargava & Tomar, 1982).

In the recent past, specific gravity of tubers has been considered an easy means of estimating yield potential of sweet potato cultivars (Bryant, 1979) and their quality characters like starch value and dry-matter content (Ishikawa & Sakai, 1973). Bryant (1979) separated sweet potato tubers with low and high specific gravity at planting time by determining whether or not they floated in water, and observed that the floaters gave 20% higher yield than the sinkers. As this simple test claimed to hold promise for selecting higher-yielding sweet potato genotypes, it was decided to scan its usefulness at the College of Agriculture, Dholi, where a large collection of sweet potato germ plasm is being maintained for research needs.

The production of haploids in large numbers is of great value to plant breeders and geneticists and this has led to the development of new techniques for haploid production (Nitzsche & Wenzel, 1977). In cultivated barley, Hordeum vulgare, there are four principal methods of isolating haploids: the culture of microspores, the isolation of embryos following the interspecific hybridization of Hordeum vulgare with H. bulbosum, ovule culture and the use of the haploid initiator gene (Kasha & Reinbergs, 1982). The present paper focuses attention on the use of the haploid initiator gene (hap) and compares this method with the H. bulbosum and microspore culture methods of haploid production.

Vegetative multiplication of potato is used routinely to produce disease-free seed tubers and to multiply new potato varieties for trials. The conventional methods of vegetative propagation using virus-tested stem cuttings allow production of 800–900 plants from a single plant in 3 years (Hussey & Stacey, 1981). Use of in vitro propagation allows much more rapid rates of multiplication of new varieties of potatoes (Wooster, 1984). Axillary buds taken from a few tubers can be multiplied to 500 plants within 4 months by repeated subculturing of nodal cuttings on artificial media in sterile conditions.

Major economic losses in many agricultural crops have been attributed to damage caused by insects of Heliothis spp. For example, Alcock & Twine (1980) estimated that in Queensland, Australia the annual losses caused by Heliothis spp. were over $16 million, with major losses in sorghum, cotton, tomatoes, tobacco, and safflower. The increasing resistance of Heliothis spp. to pesticides together with an increasing awareness of environmental problems associated with excessive use of pesticides has encouraged the development of research into the area of host-plant resistance. Naturally occurring toxicants and repellants, feeding deterrents and sex pheromones have been evaluated for some years (Jacobson, 1982; Lukefahr, 1982).