Correlations within and between characters between and within generations as a measure for the early generation selection in potato breeding

Summary The main objective was to determine the reliability of selection in early generations of a potato breeding programme. To that end data were recorded in the seedling generation, an early and a late harvested experiment of the first clonal generation and the late harvested second clonal generation on up to 30 genotypes of 55 populations from crosses of three Solanum tuberosum ssp. tuberosum cultivars and seven selected S. tuberosum ssp. andigena clones, adapted to the northern temperate zone. Phenotypic correlations were computed per population in almost all possible combinations within and between characters between and within generations. The mean across 55 comparable correlation coefficients was considered to be the best estimate of the relationship concerned.In all four experiments data were collected on number of tubers, tuber yield and mean tuber weight; in the three experiments of the two clonal generations in addition on date of emergence, number of stems, plant height, haulm type, and general impression of the underground plant parts and in the two late harvested clonal generations on date of maturity and under water weight.The results confirmed that general impression which is largely decisive for the selection in early generations, is a little reliable measure. However, from the magnitude of the mean correlations between experiments within characters it must be concluded that selection for most of these separate characters is hardly more reliable. An exception was date of maturity for which a mean correlation was determined of r=0.78 between the two clonal generations. The second strongest mean correlations, perhaps surprisingly, were for tuber yield, viz. r=0.52 between the seedling generation and the late harvested first as well as the second clonal generation and r=0.63 between the late harvested clonal generations. From the correlations between characters it appeared that for a high tuber yield, besides its components, in particular an early emergence, a large plant height, an attractive haulm type and a late maturity are of importance.The main conclusion is that, as long as not enough seed tubers are available for the layout of statistically sound experiments, a negative instead of a positive selection should be applied to avoid the rejection of most of the valuable genotypes in an early stage. On the basis of the results directives for the application of such a negative selection are given.     

春马铃薯种薯大小对其植株性状及产量的影响研究

该文选用过翻秋的小整薯作种进行春播试验，探讨了不同大小种薯对植株性状和产量的影响及其经济效益。结果表明，从植株性状和产量上看，每窝种薯数在１－４范围内，随着种薯数的增加，每窝基本茎数增加，出苗后第３０天冠层覆盖度增加，株高降低，茎粗变细，结薯数增加，埠茎产量变化不大，单个块茎重减少，大中薯数变化不多，大中薯重下降，大中薯数率和大中薯重率降低，其中每窝和薯数与基本茎数，出苗后第３０天的冠覆盖，株高，     

Components of Visual Selection in Early Clonal Generations of a Potato Breeding Programme

In the first two clonal generations of a potato breeding programme, clones are visually selected for ‘plant appearance’. Selection for plant appearance based on unreplicated small plots is unreliable, due to significant genotype × environment interaction and high error variance. In order to improve the selection efficiency, component traits of plant appearance were identified and the effect of selection for these components was studied. Tuber yield was found to be the principal component of plant appearance while stolon length and tuber appearance contributed significantly, but to a lesser extent. Tuber yield had a higher heritability than plant appearance. Characters determining the appearance of stolons and tubers were found to have equal or lower heritabilities than plant appearance at 80 days after planting and somewhat higher heritabilities than plant appearance at 145 days after planting. Hence, since the expected and observed selection responses of the component characters have been found to be equivalent to that of plant appearance, selection for plant appearance cannot be improved upon by separately selecting for characters like tuber yield and tuber appearance.     

The effect of seed tuber weight on characters in the first and the second clonal generation of potato populations

Summary Fifty-five populations from crosses of three Solanum tuberosum ssp. tuberosum cultivars and seven selected S. tuberosum ssp. andigena clones adapted to the northern temperate zone have been studied in the seedling and the first and second clonal generation. This paper only deals with the effect of seed tuber weight on various important agronomic characters which are selected for in early clonal generations, independently of the type of crosses.The results showed that a distinction has to be made between the effects of differences in seed tuber weight within and between seedlings, i.e. genotypes. The effects on the first clonal generation of differences in weight of the tubers within seedlings and those of the first heaviest tubers between seedlings were similar and comparable to seed tuber weight effects within cultivars. In contrast to the within seedlings effects the between seedlings effects proved to be heritable. This is concluded from the fact that, on average, independent of seed tuber weight seedlings with larger first heaviest tubers performed better in the second clonal generation than those with smaller ones. Notably plant height, general impression, date of maturity and particularly tuber yield and mean tuber weight in the second clonal generation were related to the weight of the first heaviest tubers of the seedlings. The potentialities of these findings for an early generation selection are discussed.     

Selection for yield in small plots of spring wheat

Summary Four selection experiments were sown: single-row plots with single row-spacing (20 cm), single-row plots with double row spacing (40 cm), three-row plots and six-row plots both with single row-spacing (20 cm). Selection entries were mimiced by 16 different varieties or advanced breeding lines, which were also sown in a yield trial. Each experiment was laid out as a 4-times replicated randomized block design. Row length was 2 m. Alley borders and border-rows of multiple-row plots were harvested separately to evaluate the effects of different harvesting procedures on the selection efficiency. Removal of alley borders was found to be disadvantageous, since the gain in precision was more than offset by the loss in sampled area. Wide spacing of single-row plots improved the selection efficiency in comparison with normal spaced single-row plots. In multiple-row plots the selection efficiency was not improved by harvesting only the central rows.For gross plot yield (= yield of net plot + yield of alley borders) the differences in selection efficiency between the various selection plot-types were explained on the basis of the genetic variance, the environmental variance and the coefficient of genetic correlation with farm yield as determined in the yield trial.     

Early generation selection for potato tuber quality in progenies of late blight resistant parents

Developing disease resistant cultivars is one of the major objectives for a potato (Solanum tuberosum L.) breeding program, but many resistant clones have not achieved commercial acceptance because of late maturity and non-marketable tuber characteristics. Selection for tuber quality should have greater emphasis inbreeding disease resistant cultivars. The objectives of this study were 1) to evaluate the ability of late blight (Phytophthora infestans (Mont.) de Bary) resistant parents to transmit chip-processing (tuber appearance, specificgravity, and chip-color) or tablestock (tuber appearance) quality to the offspring and 2) to compare selecting for tuber quality in single-hill versus eight-hill generations. We made crosses among eight unadapted potato cultivars (B0718-3,Bertita, Bzura, Greta, Libertas, Stobrawa, Tollocan, and Zarevo) with reported late blight resistance with adapted susceptible cultivars/breeding clones to generate 95populations (4,750 seedlings). Approximately 10% of the progeny from each cross were selected from single-hill plots based on tuber appearance, number, shape, and internal defects. These selected clones (408) were evaluated for tuber appearance, specific gravity, and chip-color. The same evaluations in the following year were made on tuber samples from eight-hill plots. Libertas and Tollocan were the best parents for transmitting chip-color; B0718-3, Zarevo, and Tollocan for transmitting tuber appearance; and Bzura, Libertas, and Zarevo for transmitting high specific gravity to the highest percentage of the offspring. Overall, 50% and 56% of the clones based on single- and eight-hill generation, respectively, were considered to possess chip-processing quality; over 90% of the clones had acceptable tablestock quality. A total of 71% of the clones possessing acceptable chip-processing and 95% of the clones possessing acceptable tablestock quality selected in both generations were identified in single-hill plots. The evaluation of tuber quality characteristics in single-hill generation not only permitted the identification of clones with acceptable chip-processing and tablestock, but also increased the amount of clonal information for the following generation of selection. In crosses between late blight resistant and susceptible clones, selection for tuber quality traits can be initiated in single-hill generation using a moderate selection intensity and precede late blight testing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preventing chimerism in potato (Solanum tuberosum L.)

Summary A fast neutron irradiation experiment using two different dose rates has been performed on the potato variety Desiree in order to obtain chimera-free mutants. Both tubers and tuber parts (cross sections) were de-eyed at different moments before and after irradiation. Adventitious sprouts successively developing on the callus in the holes of excised eyes were separated from the treated tubers and planted individually. So called grouped sprouts were separated. Results indicated that (practically) chimera-free mutants can be obtained by de-eying tuber parts shortly before irradiation, by applying relatively high dose-rates and by taking adventitious sprouts which develop not earlier than three months after irradiation.Separation of the grouped sprouts demonstrated that each part originated from a single original cell.This article is dedicated to Dr F. P. Ferwerda who till September 1969 was in charge of potato mutation research at our Institute.     

Genotypic variation for root pulling resistance in potato and its relationship with yield under water-deficit stress

Summary An extensively distributed root system may reduce the probability of crop failure during periods of restricted water supply. A quantitative measure of root distribution in the soil profile, i.e. pulling resistance of roots (PR), was tested at two moderately droughted tropical field sites. A total of 250 genotypes were evaluated for PR, 45 days after planting and for tuber yield at harvest at separate sites and years. The need to use genotypes adapted to a specific location for comparisons, across sites or seasons was shown by the results of a random analysis of variance model partitioning across site-season, location, and year effects for PR and tuber yield.A combined PR and growth analysis on 31 early-maturing clones, 7 of which had tubers at the time of sampling, gave significant correlations between PR and root length, dry weight of pulled and residual roots, plant height, number of stems, and in the case of the 7 genotypes with tubers, tuberlet weight and number. A regression model to predict PR based on growth analysis data is presented. Neither tuberlet weight nor number contributed significantly to the prediction once root characters and vigour-related characters were incorporated. Variation for PR among clones was significant and the means ranged from 0 kg/plant to 37 kg/plant during the 3 trials. High PR was evident in both early and late maturing clones. Drought resistance (DR), defined as high yielding ability and high PR under water deficit conditions, of the clones Huinkul and MS-35.22.R was superior to that of the high-yielding and adapted LT-7 check, while moderate levels of DR were confirmed for the clones BR-63.15, Cruza 27, Haille, and MEX-21. Tuber yield and PR under moderate drought were significantly correlated (r=0.569^***), which suggests that the PR method can be utilized to assist in the selection of high-yielding, drought resistant, potato genotypes adapted to tropics.     

The effect of low plant density on response to selection for biomass production in switchgrass

Switchgrass (Panicum virgatum L.) is a model bioenergy species with a high biomass production from which renewable sources of fuel and electricity can be generated. The objective of this study was to perform divergent single-plant selection for biomass yield at low plant density, intermate the selected plants in polycrosses, and evaluate the performance of their half-sib (HS) progenies in sward and row plots. One thousand plants from Alamo and Kanlow populations were planted in unreplicated honeycomb trials with a plant spacing of 120 cm. Moving-ring selection was applied to select 15 high- and 15 low-yielding plants from each population. These were grown in separate polycrosses to create HS-families. Four HS-families from high- and 4 from low-yielding parents of Alamo and Kanlow, along with their bulks were evaluated for 3 years in sward plots with row spacing of 18 cm. Five HS-families from high- and five from low-yielding parents of Alamo and Kanlow were evaluated for 2 years in row plots spaced 76 cm along with their bulks. Overall, the row-plots had 20% higher biomass per unit area than the sward-plots. Across populations and plant densities, the highest-yielding HS-families produced between 2.0 and 9.3 t/ha more biomass than the lowest-yielding HS-families. The mean biomass of the HS-families from parents selected for high-yield was between 0.34 and 4 t/ha higher than the mean of the HS-families from the low-yielding parents. The annual response to selection for the mean and the bulk of the HS-families from the high yielding parents was 19 and 27% higher than the check. These results indicate that on average, high- and low-yielding parental genotypes were effectively selected from the two populations under low plant density.     

Combining ability analysis and correlation between breeding values in true potato seed

True potato seed (TPS) requires the selection of appropriate parents for developing hybrid offspring. Parents for routine crossing schemes need to be selected according to their combining ability. Hierarchical and factorial mating designs provide a mean values to assess the general combining ability (GCA) of clones included in crossing schemes. Furthermore, specific combining ability (SCA) may be investigated using the factorial mating design. The aim of this research was to determine the combining ability of clones included in early and intermediate TPS breeding populations developed by the Centro Internacional de la Papa (CIP). Likewise, correlations between breeding values (or additive genetic correlation, p_A) were calculated. Two hierarchical mating designs (in both the early and intermediate populations) and one factorial mating design (in the intermediate population) were evaluated in two contrasting Peruvian locations (La Molina ‐ coastal desert, and San Ramon, warm humid tropics). Plant and tuber characteristics were recorded in these experiments. Significant GCA was observed for tuber yield in all experiments. The male's p_A between plant vigour after transplanting and tuber yield was significant, thereby suggesting that offspring with early vigorous growth are high yielding. Plant vigour was also correlated with tuber set, but only among the breeding value of female parents, which suggests that high tuber yield could be achieved because offspring with early, vigorous growth have many tubers. High tuber yielding hybrids can be obtained by choosing parents with significant GCA, whose tuber yield can also be further enhanced if the crosses have a significant SCA.     

Somaclonal variation in explant-derived potato clones over three tuber generations

Summary Tuber characteristics of potato clones (Solanum tuberosum L.) regenerated from cultured leaf, rachis or stem pieces of cv. Desiree were assessed in field trails over three years. In the first two seasons, when the crop was grown for seed potato production, tuber numbers and the tuber yields were normally distributed and the population means of the clones were about the same as those of the controls. When 78 of the clones were grown as a ware crop in a replicated field trial there were statistically significant differences between most clones and the controls in total yield (generally lower) and ware yield (generally higher), brought about by alterations of the size distributions of tubers. In all years the population of clones had fewer scab (Streptomyces scabies) lesions than the controls. Clones with consistent differences in flesh colour and eye depth were also observed. Two out of 78 clones, in 1984, had significantly higher dry matter content. No stable decrease in susceptibility to the cyst nematode Globodera pallida was observed amongst 167 clones tested. These potato plants regenerated from explants clearly show that somaclonal variation can include agronomically relevant changes.     

Enhancement of diploid Solanum chacoense Bitt. using adapted clones of Solanum phureja Juz. & Buk.

Summary F₁ hybrids between Solanum phureja and S. chacoense were studied in a new approach to enhance wild diploid potato species using adapted S. phureja clones as the female parent. S. chacoense parents had few tubers, whereas S. phureja parents had been previously selected for tuberization under long days. Twenty hybrid families were evaluated for haulm vigor, vine maturity, stolon development, frequency of tuberization, tuber set, tuber yield and average tuber weight under naturally occurring increasing or decreasing photoperiods in spring and fall growing seasons in Morocco. The hybrid plants were more vigorous, later maturing with thicker stolons in the spring season. Frequency of tuberization and tuber set did not vary with season. Tuber yield and average tuber weight were higher in fall; the maximum yield was 2.4 and 4.6 kg per hill under spring and fall conditions, respectively. Remarkable variation was found both between and within hybrid families for all traits in this first cycle of enhancement. The selection of vigorous, fertile clones incorporating the S. chacoense genome is possible by using S. phureja as an adapted germplasm source.     

The Response of Sweet Potato (Ipomoea batatas Lam.) to Inter- and Relay-cropping with Maize (Zea mays L.)

Four sweet potato cultivars were inter- and relay-cropped with maize at two locations in Peru. Increasing interspecific competition drastically reduced tuber yields of all cultivars; fewer tubers m ⁻² were produced and no tolerant genotype was identified. Likewise the mean tuber weight declined linearly for two cultivars when competition became severe. Shoot development was less affected. Under intense competition the plant top was favoured in assimilate partitioning to the detriment of tuber formation. Overall reduction in assimilate production due to mixed cropping was the major cause of yield loss. Various intercropping combinations were found with the same productivity but distinct proportions of the component crops (sweet potato + maize). Land equivalent ratio (LER) exceeded sole crop productivity only for the combinations with the highest maize yields. Biomass production was clearly increased by intercropping but there was no increment in marketable yields. Relay-cropping reduced tuber and maize yields and had the lowest productivity of all combinations tested.     

Combining resistance to potato leafroll virus (PLRV) with immunity to potato viruses X and Y (PVX and PVY)

Summary Degeneration of seed tubers caused by viruses is a major constraint to potato cultivation in many warm tropical areas. Cultivars resistant to the most important viruses present a promising solution to such a problem. In a breeding study conducted at the International Potato Center (CIP), ten cultivars resistant to PLRV were crossed to five clones immune to PVX and PVY, as well as to a susceptible control. The resulting progenies were screened for PVX and PVY immunity. Afterwards, the resistant genotypes were fieldexposed to a PLRV-viruliferous aphid population. One tuber was harvested from each plant and used to assess, using ELISA serology, the presence of leafroll virus. The cultivars Serrana and Pentland Crown gave the best progenies in terms of percentage of healthy plants, with values of 47.4 and 33.3 respectively. The presence of joint infection of PLRV and PVY or PVX in the progenies of the susceptible control resulted in an increased susceptibility to leafroll.     

Analysis of an incomplete diallel cross among three ssp. tuberosum varieties and seven long-day adapted ssp. andigena clones of the potato (Solanum tuberosum L.)

Summary The main aim of the experiment was to study the behaviour of seven long-day adapted clones of Solanum tuberosum ssp. andigena (A) and three varieties of S. tuberosum ssp. tuberosum (T) in an incomplete diallel cross. The four groups of crosses, TxT, TxA, AxT and AxA, held 2, 12, 20 and 21 populations, respectively. Eleven of the intersubspecific crosses were exact reciprocals. Thirty random clones per population were grown as second clonal generation in an incomplete block design with four replications in plots of two plants per clone in 1980, the parents included in many plots. Data were recorded on ten characters.The results showed that group TxA gave the highest tuber yield and AxT the second highest. The F-values indicated highly significant genotypic effects for all characters in all populations. The mean genotypic coefficients of variation (GCV), were the highest for group AxA for all characters. The ANOVA, based on population means showed significant mean squares for general combining abilities (GCA) and for differences of reciprocalls for all characters; the specific combining ability (SCA) mean squares were significant only for date of emergence, plant height and haulm type. Almost all GCA effects of the parents were significant positive or negative. Several populations showed also significant SCA effects. The correlations between the GCA effects and the parental values were of about the same magnitude as the heritabilities; those between the population means and the midparental values were slightly lower.Compared to the midparental values, most populations showed significant positive heterosis for date of emergence, haulm type, number of tubers and under water weight; all populations had significant negative heterosis for mean tuber weight and nearly all for plant height and general impression. All populations from groups TxT and AxA had significant negative heterosis for tuber yield and so had 13 out of the 20 populations from group AxT, while seven of the 12 from group TxA showed significant positive and four significant negative heterosis. The average heterosis for tuber yield of group TxT was –11%, of TxA 3.4%, of AxT–9% and of AxA–18%. The highest mean tuber yields were obtained from crosses with a very high yielding A-parent as female, while the heterosis was negative. Though significant differences between the 11 reciprocals occurred for all characters, consistent differences occurred only for tuber yield. Averaged over the 11 crosses the TxA populations outyielded their exact reciprocals by 10.7%. For the highest tuber yields in A-T crosses, therefore, the tuberosum cytoplasm seems to be preferable. By contrast for a high male fertility the andigena cytoplasm is preferable.     

甘薯实生系与其无性系性状相关关系及早期选择利用研究

甘暮实生系是分离世代,其性状的变异与资源品种表现同一趋势,与其无性系在诸多性状上呈强弱不同的正相关关系,这是对实生系进行早期选择利用的基础.根据结薯性可将实生系分为成薯、膨大和直根3个类型,成薯系%因组合而异,受环境影响不明显.5年的研究结果证明:无性系类型间的产量性状有明显差异,从成薯类型选育高产新品系的入选率高.在此问题上和美国Granberry.M.等的认识不同.建议把我国甘薯育种的初选期提早到实生系时期,以缩短育种周期,提高育种效率.笔者认为把甘薯杂交种子培育的株系,定名为实生系,比较确切.     

甘薯主要数量性状对单株产量的通径分析

用秦薯1号自交后代实生苗为试验材料,试验对甘薯的分枝数(x1)、最长蔓长(x2)、分枝总长(x3)、节间长(x4)、蔓粗(x5) 、叶面积(x6)、单株绿叶重(x7)、藤叶重(x8)、单株薯数(x9)、单薯重(x10)、根冠比(x11)和单株产量(y)12个数量性状进行了测定。通过相关分析、逐步回归和通径分析表明单株绿叶重对单株产量的影响最大;单株薯数和单薯重对单株产量的直接作用较大。高产育种以单株产量为选择目标时,应以单株绿叶重、单株薯数和单薯重的选择为主,结合根冠比、分枝数、叶面积和蔓粗,对这7个性状进行综合考虑和选择。     

Effectiveness of in vitro selection for agronomic characters in potato

Effectiveness of in vitro selection for agronomic characters was studied by finding correlation coefficients between in vitro and in vivo performance of 22 potato genotypes. Evaluation was performed under eight in vitro and two in vivo conditions. Genotypic differences were highly significant for various characters under all in vitro and in vivo conditions. Error mean squares were much lower in in vitro experiments than in in vivo experiments. In vitro selection was found to be highly effective for tuber colour, stem pigment and number of eyes, and moderately effective for average tuber weight, plant vigour and foliage senescence under specific conditions. The results also indicated the possibility of in vitro selection for heat tolerance. For tuber yield and number of tubers, effectiveness of in vitro selection was low to very low, because differences in phenotypic expressions of genotypes were much enlarged under in vitro conditions compared to under in vivo conditions. Correlation coefficients for certain characters were better when in vitro conditions were closer to in vivo conditions. To improve the efficiency of in vitro selection, there is perhaps a need to simulate and identify the in vitro conditions under which genotypic differences are reflected in phenotypes more realistically as they are expressed under in vivo conditions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic analysis of,and selection for,factors affecting quantitative resistance to Xanthomonas campestris pv. oryzae in rice

Summary This study assessed 46 potato cultivars, breeding lines and Solanum spp. for heat-tolerance using short-term growth rates and carbon assimilation measurements of young in-vitro-derived plants. Plants of the 46 clones and species were transferred from greenhouse conditions to controlled conditions set at 33/25°C day/night with 12 h photosynthetic photon flux density (PPFD) at 430–450 mol m^-2s^-1 and an 8 h daylength extension (6 mol m^-2s^-1), to inhibit tuberization. Twenty eight accessions were also grown in a 20/10°C controlled environment. Plants were harvested after 10 and 20 days and dry weights of the plant components were measured for plant growth analysis. Gas exchange (leaf net photosynthesis and maintenance dark respiration) and leaf chlorophyll fluorescence parameters (O, P, and T) were measured at 30°C. Amongst the 30 accessions grown at both hot and cool temperatures, only two accessions (Yungay and AVRDC 1287.19) produced more dry weight in the hot chamber than the cool chamber. Hot/cool ratioss for net assimilation rate (NAR) and relative growth rate (RGR) exceoded unity in five and six accessions, respectively. For the 46 accessions grown under hot conditions, none had significantly greater values than those of the control clones for RGR and NAR. Differences between clones in maintenance respiration and net photosynthesis were more closely related to RGR, NAR, and total dry weight (TDWT) in clones which invested more dry weight in leaves and less in stems. Attributes of the chlorophyll fluorescence curve did not explain more of the clonal variation in RGR, NAR, and TDWT than did gas exchange parameters. No single gas exchange or fluorescence character explained more than 50% of the variability among clones for NAR, RGR, or TDWT, but combination of favourable attributes could improve potato heat tolerance in the future.     

Studies on maturity,yield, under water weight and some other characters of potato progenies

Summary In 1965 the relation between maturity, tuber yield and under water weight was studied in 756 unselected fourth-year potato clones of twelve crosses. Other characters studied were seed potato weight, date of emergence, plant height, general impression of the tubers at lifting, tuber weight and payment weight, as the above relation could be influenced by or depend on these characters.The experiments were carried out on a clay soil at Wageningen. The experimental design was a partially balanced lattice with four replications and five plants per plot.The clone means, corrected according to F-values for blocks, were used for determinating normal correlation coefficients between all possible combinations of characters per population as well as for composition of frequency distributions and of population means with coefficients of variability. To estimate heritabilities within the populations the separate data of the four replications per clone were used.In 1966 the investigations were continued with 136 selected clones on both clay and sandy soil. In addition to the statistical operations used in 1965, normal correlation coefficients were calculated between the years and between the soil types using corrected clone means. The results are given and discussed.