Potato minitubers: Technology validation in Mexico

The effects of four previously reportedin vitro tuber-inducing modified culture media on the potato cultivars Atzimba and Juanita were studied under three illumination regimes. Tuberization from stem segments started 7–18 days after transfer for all the cultivar-light-medium combinations, but this early start was not related to tuber yield. Atzimba tuberized more than Juanita (1.0 and 0.8 tubers/plant respectively), and 8 h light was optimal. The medium by Wang Hu (WH) promoted the greatest tuberization for cultivar Atzimba (1,198 mg/plant) and that by Palmer-Smith (PS) for Juanita (290 mg/plant). The modified Stallknecht’s (ST), on the contrary, slightly stimulated tuberization under all illumination conditions. The presence of cytokinins and light favored the tuberization process. Dormancy was not observed in any of the microtubers, regardless of the tuber-inducing treatment.     

Variability for photoperiodic reaction among diploid and tetraploid potato clones from three taxonomic groups

The photoperiodic behaviour of 18 potato clones from three taxonomic groups (Andigena, Phureja, and Tuberosum diploid and tetraploid) was studied under controlled environments. Day lengths of 11, 13, 15, and 17 hours were provided with all other environmental conditions common. Six characters were studied: tuber formation, stem height, haulm weight, tuber number, tuber weight, and tuberization efficiency (tuber weight/haulm weight). All clones showed well defined critical daylength values at which tuberization was either absent or irregular. A wide variability for critical day length was observed among clones, the higher values corresponding to Tuberosum tetraploid and the lower values to the Phureja group. Stem height and haulm weight increased as photoperiod increased. Tuber number remained practically the same for all groups but Phureja which showed an inverse relationship. Tuber weight decreased as daylength increased for the groups Andigena, Phureja, and Tuberosum diploid which on the average showed a short day reaction for tuber yield. Tuberosum tetraploid did not show any significant change, behaving as a day neutral type. Tuberization efficiency was, in general, decreased as daylength increased suggesting a short day behaviour for all groups. A regression analysis of tuber yield and tuberization efficiency on photoperiod indicated that, in general, tetraploid genotypes were less sensitive to drastic increases in daylength than diploids.     

Effects of photoperiod on kinetin-induced tuberization of isolated potato stolons culturedin vitro

Are short-day (SD) conditions inductive or permissive for potato tuberization? This question was addressed using anin vitro culture system. Kinetin induction ofin vitro tuberization in potato stolons cultured in the dark can be partially inhibited by light treatments. Photoperiod required for a major inhibition varied with cultivars: 8 hours for cv. Red Pontiac and 16 hours for cv. Kennebec. Short photoperiods decreased kinetininduced tuberization for all cultivars. Stolons cultured on kinetin-free medium generally did not tuberize, regardless of light treatment. Effects of kinetin and photoperiod on stolon and tuber development are observed. Relationships among kinetin, photoperiod and tuber-inducing stimulus produced under short days are discussed.     

General characteristics of coumarin-induced tuberization of axillary shoots ofSolanum tuberosum L. culturedin vitro

Coumarin readily stimulates tuberization of cultured axillary shoots obtained from etiolated potato sprouts. Adequate concentrations of coumarin must be continuously present in the medium to effect tuber initiation. High nitrogen, gibberellic acid, abscisic acid, indole acetic acid, or naphthalene acetic acid reduced or inhibited coumarin-induced tuberization. Gibberellic acid and high concentrations of nitrogen in medium inhibited the uptake of coumarin-3-14C by the. axillary shoot. Based on the data of physiological activities by coumarin in other plant species and our data on tuberization, we propose that coumarin may represent in part the unknown inhibitor responsible for tuber initiation with reference to the inhibitor/gibberellic acid ratio theory of tuberization.     

Genetic variation in a population of tetraploid potatoes: Tuber resistance to the tobacco flea beetle

Variation in resistance to tuber damage by the tobacco flea beetle,Epitrix hirtipennis (Melsheimer) was investigated for progeny from a group of parental clones from the USDA potato breeding program. Each of nine clones, used as males, was crossed with three different clones, and the family responses were measured in field tests (Lubbock, Texas, 1967 and 1968) by counting tuber pits made by the flea beetle larvae. Statistically significant differences among families were found. The differences were due mainly to the male parents, since the male variance component, σ _M ² (0.470±0.235), was larger than the variance component of females mated to the same male, σ _F(M) ² (0.080±0.057). Theoretically, each of these components contains one-fourth of the genetic additive variance, and therefore, should be nearly equal if digenic, trigenic, and quadrigenic effects are small (and if no maternal effects are present). Apparently the male and female parents did not, in relation to the frequency of alleles controlling response to the flea beetle, represent the same genetic population. Heritability on an individual basis, calculated with 4 σ _M ² as numerator, equals 0.64±0.36; and at a 10% selection level the genetic advance value predicted for individual selection equals 1.896 SD units. If 100 males were crossed to one female each, and 20 progeny per family tested in 10 replicates, the genetic advance value predicted for selecting the best 10 males on the basis of their family performance equals 0.976 SD units. Thus individual or phenotypic selection appears to be more effective than selection based on half-sib progeny tests.     

Heritability of Yield Components Under Irrigated and Drought Conditions in Andigenum Potatoes

Drought is one of the major abiotic factors that affect potato production in the tropics and sub-tropics. Molecular plant breeding offers promising opportunities for developing drought tolerant cultivars, but genetic gains to be achieved through breeding depends strongly on the genetic variance and heritability of traits used in the selection process. In the present study, genetic variance and heritability of tuber yield and its components were estimated in the native potato cultivar group Andigenum, expected to include promising drought tolerant progenitors. Twenty-seven full sib families obtained from crossing 18 parents arranged in 3 mating sets were grown under irrigated and terminal drought conditions. Heritability for tuber yield, estimated from female to male variance components was 0.68 and 0.41, respectively, in the irrigated treatment, and only 0.18 and 0.06 under drought conditions. Tuber number was highly significantly correlated to tuber yield but the heritability of this trait (estimated both from female to male variance) was lower than yield heritability and its non-additive genetic variance was higher than its additive genetic variance, particularly when estimated from the female variance component. Heritability of average weight per tuber estimated for male variance component was very high under both irrigated and drought conditions. Its additive genetic variance was much higher than its non-additive genetic variance. However, average weight per tuber correlated to tuber yield within parents but not within families. These results indicate that selection for increased tuber yield under drought conditions in the Andigenum cultivar group may be slow due to its low heritability and high value of non-additive genetic variance. They also suggest that yield components may not be useful as indirect selection criterion for yield, because of their low heritability and/or poor association with yield. The identification of drought tolerance related traits with high heritability and closely associated to tuber yield under drought is consequently required to improve adaptation of potato to drought-prone conditions and efficient utilization of Andigenum potatoes for this purpose.     

Inheritance of tuber traits from phureja in diploid phureja - Tuberosum hybrids

Heterosis and combining ability for tuber number, average tuber weight, and total yield were evaluated in Phureja - haploid Tuberosum diploid hybrids. Heterosis estimates suggest dominance for high tuber number and low average tuber weight in Phureja. Total yield of the hybrid population exceeded the high parent. The higher-yielding segment of hybrids had a significantly higher number of smaller tubers per plant. Breeding value could be improved by attaining high yield with a lower number of larger tubers per plant. General combining ability was the only significant source of variation for tuber number and average tuber weight indicating high heritability. Phenotypic recurrent selection should be an effective approach to manipulating these traits. General and specific combining ability were significant for total yield. Full exploitation of genetic variance for yield will require test-crossing.     

The effect of nitrogen on the coumarin-induced tuberization of potato axillary shoots culturedin vitro

Coumarin-induced tuberization was studied on axillary shoots excised from etiolated potato sprouts each of which was cultured in vitro. Sprouts grown on culture medium with high nitrogen concentrations produced axillary shoots which elongated and would not readily tuberize. Sprouts cultured on medium low in nitrogen produced axillary shoots which tuberized with limited elongation. Carbohydrate concentration of the culture medium for the excised axillary shoot could significantly modify the nitrogen effect of the potato sprout medium. Axillary shoots growing on high nitrogen medium did not tuberize except in cases where the carbohydrate concentration was increased.     

Characterization of a new gibberellin related dwarfing locus in potato (Solanum tuberosum L.)

Gibberellins have been shown to be involved in such important processes as seed germination, flowering, maturation and tuberization in potato. Parents fromSolanum tuberosum Groups Andigena and Tuberosum were found to produce progeny containing dark green, rosette dwarf individuals which could be completely restored to normal appearance by exogenous GA₃. Test crosses indicated that this phenomenon can be explained by the action of a single locus, the dwarfing characteristic being conferred by the nulliplex condition. The gene symbol “ga₁” is proposed. Group Andigena dwarfs demonstrated much greater tuberization compared to their normal full sibs or dwarfs restored to normal phenotype by exogenous GA₃. The possibility that such gibberellin mutants may be involved in the long day adaptation of Gp. Tuberosum is discussed. This character may also be a useful tool for investigating various aspects of the gibberellin status of the potato.     

Improved procedures for the isolation and culture of protoplasts fromSolanum etuberosum

An efficient and convenient procedure for the isolation of protoplasts fromSolanum etuberosum is described. Excised leaves of plants grownin vitro were preconditioned for 3 days in the dark at 4 C. A 16 h enzyme digestion followed with purification by flotation in Babcock bottles produced a mean yield of 12.5 × 10⁶ protoplasts/g fresh weight. Protoplast viability as judged by morphology at the time of isolation was 89%. Liquid preculture for 1 day at 1 × 10⁶ protoplasts/ml was used prior to plating at 1 × 10⁵ protoplasts/ml and gave a mean survival of protoplasts of 43% after 8 days in culture.     

Petiole analysis and the nitrogen fertilization of Russet Burbank potatoes

The effect of nitrogen rates on the yield of Russet Burbank potatoes was studied in field experiments in Idaho. Petioles were sampled at the 6-to-8 leaf stage and thereafter at two week intervals until mid August. Petiole nitrate concentrations were very high early but decreased rapidly as the season progressed and declined to a very low level as the plants matured. The nitrate content of the petioles reflected the amount of N applied to both locations. Nitrogen applications increased total yield and the quantity of the larger size tubers. A highly significant correlation was found between the early season petiole nitrate concentrations and total yield. Suggested ranges of petiole nitrate concentrations were developed as a guide to efficient N fertilization of Russet Burbank potatoes in Idaho.     

The phosphorus requirements of five consecutive potato crops on an Andept in Rwanda

Farmers in Rwanda do not apply P fertilizer on their crops. Bray and Kurtz #1 extractable P levels are generally less than 2 ppm on these soils. Therefore, a long-term experiment was established to determine the yield response of potatoes to P fertilizer. A maximum accumulated yield of 130 t/ha in 5 crops was obtained with 902 kg/ha of P. The no P treatments produced 72% of the average maximum yield. The external P requirements, determined with P sorption isotherms, averaged 0.04 μg/ml if equilibrated at 15 C and 0.02 μg/ml if equilibrated at 25 C for the 5 crops. The residual efficiency of the applied P fertilizer was less than 20%, suggesting that large applications of P are not advisable on Andepts, which have amorphous materials because the applied P is not available for subsequent cropping seasons.     

A method for estimating the loss in tuber yield caused by late blight of potato

A method was developed for estimating tuber yield losses caused by late blight of potato (Phytophthora infestans) (Mont.) de Bary. The method is based on yield and disease data collected for the varieties Green Mountain and Katahdin grown in eastern Canada during the period 1953–1970. The percentage yield loss can be calculated for any disease progress curve. The estimated loss was within 5% of the actual loss in nine cases out of ten.     

Anatomy and compositional variation within potatoes

Re-examination of the histological development of the potato tuber supports Artschwager’s view that tuber growth is predominantly due to enlargement of the perimedullary zone and is of procambial origin. Pith (medulla) and cortical regions are differentiated from the ground or fundamental meristem derived from the apical meristem of the stolon apex, even before tuberization has been initiated. The procambium gives rise to external phloem, primary xylem, internal phloem and associated parenchyma, and likewise to interfascicular parenchyma. Those parenchyma cells so formed inwardly to the xylem “ring” contribute to the growth of the perimedullary zone. The sequence of tissue origins is diagrammed and discussed from the viewpoint of modern concepts of histogenesis.     

Influence of slit plastic mulches and nitrogen fertilization rates on potato yield and quality

Clear and black slit plastic mulches had little effect on tuber yields when compared with unmulched controls during two growing seasons. Mulching films significantly increased the incidence of pinkeye, caused byPseudomonas spp. and varius types of soft rot in 1974 but not in 1975. The incidence of tuber greening was higher than normal both years due to inability to hill with mulch films in place. Under these conditions, black plastic reduced the incidence of greening. Significant yield responses were observed for an increase in nitrogen fertilization rate from 100 (45.36 kg) to 140 (63.5 kg) but not from 140 to 180 1b, (81.65 kg) N/A. Plastic mulches did not affect the nitrogen response. Higher post-harvest inorganic soil nitrogen levels were found under both mulches compared with unmulched controls.     

Potato haploid performance in 2x × 4x crosses

Nineteen haploids (2n = 2x = 24) extracted from four tetraploids ofSolanum tuberosum (2n = 4x = 48) with high 2n egg frequencies and known mode of 2n egg formation were evaluated via 4x progeny from 2x × 4x crosses (haploid × cultivar) for total tuber yield, tuber appearance and tuber set. Ninety-eight, 4x families (15-20 genotypes each) were planted in the randomized complete block design with two replications at two locations. Analyses of variance were conducted for all haploids over three common testers, and each of the four groups of haploids individually over a variable number of testers. The performance of haploids, based on general combining ability effects, was consistent for all traits, when tested with either three or more testers. Diploid clones can be evaluated in 2x × 4x crosses using three unrelated adapted 4x testers. Nonorthogonal comparisons indicated no significant differences for all traits among four groups of haploids, and between modes of 2n egg formation. Significant variation within each group of haploids indicates that selection at the haploid level should be carried out among haploids from either the same or different cultivars. Superior haploids can be utilized in 2x × 4x and 2x × 2x breeding schemes to generate 4x clones.     

Pre and early post-emergence weed control with Paraquat in potatoes

Studies using Paraquat herbicide for early post-emergence control of broadleaved and grass weeds in Katahdin and Russet Burbank potatoes were conducted in Maine during four growing seasons. All rates and times of application of Paraquat gave good commercial control of grass and broadleaf weeds when compared to Premerge and Dowpon treatment as checks. Paraquat applied to Katahdins 2 weeks after ground crack reduced the yield of tubers but did not significantly affect specific gravity. Yield and specific gravity of Russet Burbank was reduced by Paraquat applied one and 2 weeks after ground crack. Paraquat can be used effectively for weed control in Katahdin up to one week after ground crack without crop damage. In Russet Burbank it appeared that application at ground crack was about as late as Paraquat could be applied without affecting yield or specific gravity of tubers.     

The relationship betweenVerticillium albo-atrum inoculum density and potato yield

Population studies withVerticillium albo-atrum (microsclerotial form) have shown that a significant negative correlation exists between inoculum density in field soils determined before planting and yield of potatoes in some areas of Colorado but not in others. In Southern Weld and Morgan Counties where potatoes are planted early in sandy soils, reduced yield in Norgold Russet and Norchip cultivars occurred as inoculum densities increased. In Northern Weld County where potatoes are planted later in heavier soils, no such relationship was found. The significant relationship between inoculum density and reduced yield was associated with growing areas where conditions, particularly air temperature, appear to be favorable for verticillium wilt development when plants begin to mature. A minimum number ofVerticillium propagules was required to cause significant yield reductions in total, marketable and U.S. No. 1 grade categories. Below this minimum number, no significant yield reductions occurred. In Southern Weld and Morgan Counties, this minimum number was found to lie between 17.5 and 23 propagules per gram of soil. Controlled greenhouse studies showed that as air temperature decreased from 29.4 C (85 F) to 23.9 C (75 F) more inoculum was required to cause significant disease expression and to shorten plant life. This study has shown that in some areas soil inoculum assays prior to planting may provide a basis for selecting fields which are safe for planting potatoes to avoid severe losses from verticillium wilt. Furthermore, they may help in identifying fields where preventive control measures may be required for satisfactory potato production.     

The genetic basis for tuber greening in 24-chromosome potatoes

Greening of potato (Solarium tuberosum L.) tubers is often a problem in retail markets. An experiment was performed to study the mode of inheritance of tuber greening in 24-chromosome potatoes. Tuber greening was determined to be quantitatively inherited. Genetic and environmental variance components were calculated. Tuber greening inheritance is due to additive and epistatic effects. Epistatic effects accounted for 59% of the genetic variance. No dominance or maternal effects were observed. Narrow sense heritability was 0.27 and broad sense heritability was 0.66 after location, block, and genotype by environment interactions were removed. Broad sense heritability for tuber greening is large enough to permit effective selection against tuber greening in potato breeding programs when epistasis can be fixed.