G. R. Mackay

The effect of storage temperature on reducing sugar concentration and the activities of three amylolytic enzymes in tubers of the cultivated potato, Solanum tuberosum L.

SummaryReducing sugar content, and activities of three starch hydrolysing enzymes, alpha-amylase, beta-amylase and debranching enzyme were measured over several months in tubers of five cultivars stored at 4°C or 10°C. Cultivars differed in their sensitivity to storage temperature. Reducing sugar content of tubers and the activities of three starch hydrolysing enzymes increased sharply during the first weeks of storage at 4°C. At 10°C, reducing sugar content, and the activity of the three enzymes remained constant or increased only slightly.

Use of mid-parent values and progeny tests to increase the efficiency of potato breeding for combined processing quality and disease and pest resistance.

A potato breeding strategy is presented which avoids the common but ineffective practice of intense early-generation visual selection between seedlings in a glasshouse and spaced plants at a seed site. Once pair crosses have been made, progeny tests are used to discard whole progenies before starting conventional within-progeny selection at the unreplicated small-plot stage. Clones are also visually selected from the best progenies for use as parents in the next cycle of crosses whilst they are multiplied to provide enough tubers for assessment of their yield and quality. Mid-parent values, as well as progeny tests, are then used to select between the resultant crosses. Material from other breeding programmes can be included in the parental assessments and used in the next cycle of crosses if superior. Finally, in seeking new cultivars, the number of clones on which to practise selection is increased by sowing more true seed of the best progenies, but without selection until the small-plot stage. Traits considered are resistance to late blight [Phytophthora infestans (Mont.) de Bary] and to the white potato cyst nematode [Globodera pallida (Stone)], fry colour and tuber yield and appearance, as visually assessed by breeders. The theoretical superiority of the strategy for seeking new cultivars lies in being able to practise between-cross selection for a number of economically important traits within 1 or 2 years of making crosses, something that is not possible on individuals as seedlings in the glasshouse or spaced plants at the seed site. This also means that full-sib family selection can be operated on a 3-year cycle, an improvement on current practice of clonal selection on what is often at least a nine-year cycle. New cultivars can be sought with more confidence from the best progenies in each cycle, and modern methods of rapid multiplication used to reduce the number of clonal generations required to find the best clones.

Amylolytic activity in stored potato tubers. 2. The effect of low-temperature storage on the activities of α-and β-amylase and α-glucosidase in potato tubers

SummaryTubers of the potato cultivars Record, Wilja, Pentland Dell and Brodick (formerly clone 137371) were sampled before and after storage at either 4°C or 10°C. Reducing sugar content stayed constant during storage at 10°C in all four cultivars but rose greatly during the first 6–12 weeks of storage at 4°C in Record, Wilja and Pentland Dell but not in Brodick. Amylolytic activity was determined after 5 weeks storage using blockedp-nitrophenyl maltoheptaoside as substrate for α-amylase,p-nitrophenyl maltopentaoside as substrate for β-amylase, andp-nitrophenylglucopyranoside as substrate for α-glucosidase. The values obtained from tubers stored at 4°C were higher than those from tubers stored at 10°C, the differences being much less in Brodick than in the other three cultivars.

The integration of protoplast fusion-derived material into a potato breeding programme — a review of progress and problems

This paper reviews investigations into the application of protoplast fusion to the genetic and agronomic improvement of potato. Fusion studies involving Solanum tuberosum are reviewed under the categories of: fusion with wild relatives, dihaploid fusion and asymmetric strategies. The selection and characterisation of putative somatic hybrid material is identified as a critical stage in the process and certain specific aspects of this technology are identified. Future prospects for the wider uptake and integration of these techniques into breeding programmes are also discussed.

Potato starches: variation in composition and properties between three genotypes grown at two different sites and in two different years

Starch granules were isolated from three distinct potato (Solanum tuberosum L) genotypes, cvs Glamis and Record and line 86Q35(8), grown at two different sites in 1996 and 1997. Differences in the chemical compositions of the granules were investigated using blue values of the starch–iodine complexes as indicators of amylose contents and from phosphorus contents. The physical properties determined were starch damage, swelling power, turbidity, granule size distribution, viscosity data and profile, and gelatinisation temperatures as well as enthalpy of gelatinisation. The differences in the blue values of the starch–iodine complexes were significant for genotype (P < 0.001) but not for site or year. Highly significant differences in starch granule phosphorus contents were found both between genotypes (P < 0.001) and between sites (P < 0.001), but the differences between years were less significant (P < 0.01). Genotype 86Q35(8) had nearly twice the starch phosphorus content of the other two genotypes. Significant differences were also found between genotypes in terms of granule size distributions (P < 0.01), with 86Q35(8) having a modal granule size smaller than that of the other two genotypes. The viscosity data and profiles, measured at 48 g l−1, showed that samples of starch granules isolated from genotype 86Q35(8), irrespective of the site or year, behaved similarly to each other. However, the profiles obtained from starch granules derived from Glamis and Record depended on the site and year and were distinctly different from the profiles obtained from starch granules isolated from 86Q35(8). On the other hand, the differential scanning calorimetric data recorded no consistent differences in the gelatinisation temperatures and enthalpy of gelatinisation between genotype, site and year. The prospects of using specific potato genotypes as sources of starch for particular uses are discussed. © 2000 Society of Chemical Industry

Progeny testing for resistance to potato virus Y: a comparison of susceptible potato cultivars for use in testcrosses with resistant parents

SummaryFor potato breeding or genetical research purposes, the number of copies of a dominant major gene for resistance to potato virus Y in a parent clone can be determined by test-crossing with a susceptible parent and observing the segregation ratio of resistant to susceptible seedlings in the progeny. In a comparison of different susceptible cultivars for use in test-crosses for this purpose, their progenies differed in the clarity of symptoms and parental phenotype proved an unreliable guide. Cvs Maris Piper, Arran Peak and Dr MacIntosh were found to be suitable tester parents, Pentland Squire less so and cv. Désirée was confirmed as having a major gene conferring incomplete resistance. It was found advisable to test-cross with more than one susceptible parent.

Screening for resistance to early blight (Alternaria solani) in potato (Solanum tuberosum L.) using toxic metabolites produced by the fungus

SummaryThe phytotoxic components of the culture filtrate of the fungusAlternaria solani Sor, which causes early blight in potato, were used in this study to differentiate between resistant and susceptible genotypes selected to represent a range of reactions when screened in the field. Detached leaflet assays, using spores and toxic metabolites from the culture filtrate, were compared with field ratings and a whole-plant glasshouse test. Rank correlations between several detached leaflet tests were highly significant (P<0.01) but the correlations between these tests and the glasshouse and field tests were poor. The disease ratings obtained in the various tests were clustered into four groups and assigned to resistance classes. For many of the genotypes there was a good correspondence between resistance classes for all test methods. Divergent results between tests were associated with foliage maturity characteristics of the genotypes.

Assessing progenies of potato for resistance to early blight

SummaryProgenies from crosses between cultivars varying widely in resistance to early blight (Alternaria solani Sor.), were assessed for resistance as true seedlings in a glasshouse in Scotland. The resistance of a representative sample of surviving genotypes from each progeny was compared with samples of the same progenies not previously exposed to the fungus, both in the glasshouse in Scotland and in the field in Israel. The exposed population was more resistant. Resistance was identified more effectively in adult plants from tubers in the glasshouse than in true seedlings and agreement between glasshouse and field assessment was better when progenies were compared rather than individual genotypes. The mid parent and progeny mean scores of the unexposed population were correlated at both sites, thus confirming that the resistance is heritable. Selecting resistant individuals at the seedling stage is suggested as a useful tool for resistance breeding, having first chosen the best parents for crossing.

Half-sib family selection for yield of digestible organic matter in kale (Brassica oleraceal L.)

SummaryFour generations of half-sib family selection for yield of digestible organic matter have been completed, from an initial population which included marrow-stem kales, thousand-head kales, curled kales, Brussels sprouts and cabbages. Relative to the mean yields of two control cultivars the population means were: 106% (gen0), 122% (gen1), 128% (gen2), 111% (gen3) and 103% (gen4). These initially encouraging and then disappointing results are discussed along with suggestions for improvements in the population improvement scheme, particularly with respect to the assessment of genotype-environment interactions.

An agenda for future potato research

SummaryThe world is changing, and the rate of change is accelerating, nowhere moreso than in the pace of scientific discovery and the advance of technology. The last thirty years have also seen substantial global changes in potato production which are likely to continue if current projections are correct. Climate change is bound to affect local weather patterns, which will influence both the epidemiology of pests and pathogens and broaden their geographic range. An agenda for future research will of necessity include much of the current agenda; research into more sustainable systems; research into new and novel resistances to biotic and abiotic constraints, combining modern cell and molecular-based technologies with classical breeding approaches and research into the genetic and biochemical bases of low temperature sweetening and dormancy control, that should lead to varieties with superior storage characteristics, particularly for processing. However, a future agenda has to retain some flexibility and a component of speculative research. Perhaps potatoes could become a source of industrial feedstock or pharmaceuticals, perhaps there is a place for cultivars produced by botanic seed in Europe? The exciting thing about research is that we cannot always predict where it will lead, and a future agenda must not curb the enthusiasm of any young scientist by too rigidly adhering to that suggested here. it is essential that scientific options are kept open.