Potential for improvement by selection for reducing sugar content after cold storage for three potato populations.

The objectives of this study were to examine the expected response to selection for reducing-sugar content after cold storage in three hybrid populations, to determine whether these populations included clones low in reducing sugars, and to investigate the effectiveness of indirect selection for chip colour based on selection of sugar content after cold storage. The three hybrid populations included: a random sample of 39 clones of Population 1, which was derived from crossing ND860-2 (a clone low in reducing sugars) with F58089 (a clone intermediate in reducing sugars); 40 clones of Population 2, which was obtained from crossing ND860-2 with Russette (a clone high in reducing sugars); and 40 clones of Population 3, which was derived from crossing Russette with F58089. Sugar content and chip colour were assessed in tubers stored for 2 months at 4 °C at Cambridge, Ontario, and at 3 °C at Benton Ridge, New Brunswick. Population 1 had a slightly greater predicted response to selection for reduction in glucose and total reducing sugars than the other two populations. This could be attributed to higher heritability estimates for Population 1, which was a reflection of smaller clone × environment interaction mean squares. The greater potential advance by selection for fructose, glucose, and total reducing sugars, was a direct consequence of its lower means for these traits. Low reducing-sugar clones were found in all three populations, indicating their potential use for the selection of low reducing sugars. Populations 2 and 3, however, would require stronger selection pressures and, therefore, large population sizes. Expected correlated responses for chip colour by selection for fructose and glucose were similar to, and sometimes exceeded, the expected direct responses in all three populations. Indirect responses for chip colour by selection for sucrose, however, were lower than direct selection responses. These results indicate that indirect selection for chip colour, by selection for either fructose or glucose content after cold storage, is as effective as direct selection for chip colour.

Uniparental inheritance of a chloroplast photosystem II polypeptide controlling herbicide binding.

The ability of atrazine to inhibit Photosystem II electron transport and the rate of electron transfer from the primary to the secondary quinone electron acceptors in the photosystem II complex were examined in triazine-resistant and -susceptible parental biotypes of Brassica campestris L. and their F1 progeny derived from reciprocal crosses. The lack of herbicide inhibitory activity and the presence of functional properties which decreased the Q- to B electron transport rate constant were inherited in parallel through the maternal parent. We conclude that the herbicide receptor protein is uniparentally inherited through the female parent. These data are discussed in relation to other studies which indicate that the binding site is a 32 000-dalton polypeptide which determines the functional properties of B (the secondary Photosystem II electron acceptor).