Variations in stolon length and in incidence of tuber roots among eight potato cultivars

The stolon length and percentage of tubers with tuber roots were compared for eight cultivars ofSolanum tuberosum L. over two growing seasons. Although stolon lengths varied considerably within cultivars, there were significant differences in the average stolon lengths among cultivars. The cultivars Norchip and Monona had the shortest stolons whereas Norland had the longest average stolons. The length of the stolon did not appear to be related to color type or time of tuber maturity. Since there was no significant difference in stolon length between years, stolon length appears to be a consistent genetic trait. There was no significant correlation between the stolon length and tuber size. The incidence of tuber roots also showed variation among cultivars, although there was significant variability between times of sampling. Recent studies have demonstrated that to maximize calcium uptake by tubers, the calcium must be placed around the tubers and stolons. Since stolon length determines the location of the tubers in the hill, the stolon length of different cultivars may need to be considered for fertilizer application, cultivation or hilling procedures. Thus, to get maximum benefit from supplemental calcium for Norchip and Monona, application would need to be made close to the main stem. However, in the other cultivars, the majority of the hill would have to be enriched in calcium to effectively supply calcium to the various tubers in the hill.     

Marker-assisted genetic analysis of non-acclimated freezing tolerance and cold acclimation capacity in a backcrossSolarium population

Random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers were used to construct a partial genetic linkage map in a potato backcross population. The population, derived from two diploid wildSolatium species (frost tolerant, able to cold acclimateS. commersonii; frost sensitive, unable to cold acclimateS. cardiophyllum), was used to map quantitative trait loci (QTL) of non-acclimated relative freezing tolerance (NARFT) and cold acclimation capacity (CAC). Precise assessment of these traits allowed distinction of small but significant differences among 35 backcross genotypes. NARFT and CAC were not correlated in the segregating population, suggesting independent genetic control for these two major components of freezing tolerance. The linkage map spanned 479.4 cM and included 77 RAPD markers and two SSR markers, with 38 RAPD and 10 SSR unassigned markers. Two QTLs for NARFT were detected in two different linkage groups, accounting for 44.0% of the phenotypic variation for this trait. Two QTLs for CAC were detected, accounting for 24.9% of the phenotypic variation for this trait. QTLs for NARFT and CAC were detected at separate genomic regions, in support of the independent genetic control of these two traits. QTLs for NARFT and CAC were detected in a linkage group identified as part of chromosome V, suggesting that such chromosome constitutes a prime candidate for fine-mapping. Due to the relatively small progeny size evaluated in this study, additional QTLs for NARFT and CAC could have been involved but not identified. Therefore, the conclusions derived from this study should be considered preliminary.     

Potential for improving freezing stress tolerance of wild potato germplasm by supplemental calcium fertilization

The main objective of the present study was to investigate the influence of supplemental calcium fertilization on the levels of freezing tolerance in different wild potato species. For this purpose, the freezing tolerance of a broad spectrum of theSolatium taxa was evaluated with and without supplemental calcium fertilization. Previous studies have shown that there is a large variation in the calcium accumulation capabilities among species and among various accessions within species. While this study confirms such variation, no direct relationship between the leaf calcium content and the improvement in freezing tolerance was found. Nevertheless, overall 45% of the species accessions had significant higher leaf calcium content and 52% of the species accessions showed a significant drop in the frost score average at the p<0.05 level. In terms of this experiment, a drop in the frost scores meant an improvement to withstand cold. One third of the frost tolerant accessions and 41% of the frost sensitive accessions showed both, a significant increase in leaf calcium content and at the same time a significant lower average frost score. The different response observed among the accessions may suggest that even though most of the accessions are able to accumulate calcium, only some of them may have the ability to benefit from the supplemental calcium. Future breeding schemes may be able to use this information for selecting clones that would respond positively to calcium fertilization in terms of frost survival. Results of this study also suggest that calcium fertilization may be used as a rather inexpensive cultural practice for protecting potatoes from frost damage. The results of the present study also suggest that soil calcium levels should be taken into consideration when freezing tolerance of potato germplasm is being evaluated.     

Identification and Selection for Tuber Calcium,Internal Quality and Pitted Scab in Segregating ‘Atlantic’ x ‘Superior’ Reciprocal Tetraploid Populations

Developing chipping cultivars with improved tuber quality and disease resistance is a major interest for breeders and the potato industry. A popular chipping cultivar ‘Atlantic’, is desired for its high yield and gravity. However, this cultivar suffers from poor internal tuber quality and high scab susceptibility. On the contrary, cultivar ‘Superior’ is known to have excellent tuber internal quality and moderately scab resistance. In addition, this cultivar is known to have high tuber calcium as compared to ‘Atlantic’. The present study intended to generate populations that can be suitable for the genetic study of tuber calcium, internal quality, common scab, and other commercially important traits such as yield, specific gravity and chip quality at the tetraploid level. Two populations obtained by reciprocally crossing the cultivars ‘Atlantic’ and ‘Superior’ were evaluated during 2009 to 2012 at Hancock, Wisconsin. Significant genotype effects and moderately low to high broad-sense heritabilities were identified for all traits evaluated indicating that the observed phenotypic variation has an important genetic component. In addition, the parents differed significantly for all traits across trials, and most genotypes performed in between the two parents but some genotypes were more extreme than the parents. Furthermore, evidence of reciprocal effects was found for some traits. In addition to learning about the genetics of these important traits we were able to identify some genotypes that combined the commercially desired traits of the two cultivars.