Phenological responses of Oryza sativa, O. glaberrima and inter-specific rice cultivars on a toposquence in West Africa

Phenological properties of rice cultivars, particularly crop duration, determine their yield potential, local agronomic suitability and ability to escape from drought. Crop duration of a given cultivar depends mainly on photoperiod (PP) and temperature, but is also affected by the crop establishment practice and environmental stresses. A sample of 84 ecologically and genetically diverse rice cultivars was sown on five dates between May and September 1997 on the flooded-lowland (transplant), hydromorphic and upland levels of a toposequence at 7^° 52′ N in Cote d'Ivoire, in order to characterize the cultivars' phenological responses. In the upland, life-saving sprinkler irrigation was applied when drought symptoms were visible. A non-replicated design augmented with four replicated checks (four replications per ecosystem) was used. Phenology was characterized by date of emergence, first heading, 50% flowering and maturity. The period from emergence to flowering was subdivided into three phases following a simple model used at IRRI to characterize germplasm for photoperiodism. For each ecosystem and cultivar, the basic vegetative period (BVP) was estimated by subtracting 30 d from the duration to flowering at the sowing date associated with the shortest duration, and expressed in degree-days (dd), assuming a base temperature of 10 ^°C. The PP-sensitive phase (PSP) was estimated by subtracting BVP+30 d from the time to flowering. PP-sensitivity (PS) was calculated from the apparent change in PSP between 12.0 and 12.5 h mean astronomic daylength during the PSP, by regression across dates. Cultivars differed strongly in BVP (300 to 1200 dd) and PS (0 to 1000 dd). The BVP was generally longer in the lowland than in the hydromorph, and mostly longer in the upland than in the hydromorph, possibly due to transplanting shock (lowland) and drought (upland). Many cultivars, particularly upland-adapted japonicas, had a greater PS in the lowland than in the upland. Principal-component and cluster analyses based on BVP and PS in each of the three ecosystems established three large and three small groups of cultivars having common phenological responses. The linkage groups were associated with ecotypes (lowland vs upland, traditional vs improved) and genetic groups (O. sativa japonica and indica, O. glaberrima, inter-specific progenies). The groups were seen to represent past selection strategies by farmers and recent breeding strategies, with respect to achieving yield stability in the various ecosystems. For example, indigenous selection strategies for O. sativa upland rices seem to have favored a long BVP, whereas from O. glaberrima, which generally has a superior initial vigor, cultivars with a short BVP have been selected. The authors conclude that the modern upland rice breeding strategy for the region on the basis O. sativa, which aims at drought escape using a short BVP, is paralleled by existing indigenous O. glaberrima materials. Efforts to utilize these materials for breeding are ongoing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification and molecular mapping of Flowering Date1 (FD1), a major photoperiod insensitivity gene in the adzuki bean (Vigna angularis)

The induction of flowering under long‐day conditions is an important adaptation by short‐day plants, such as adzuki beans (Vigna angularis), to high‐latitude environments. This study clarified the genetic control underlying the long‐day insensitivity of adzuki bean cultivar ‘Shumari’. ‘Shumari’ was found to be insensitive to a 16‐h day, whereas landrace Acc2265 was highly sensitive. When grown under natural long‐day conditions at Obihiro (42°9′N), Acc2265 initiated flowering at least 80 days after ‘Shumari’. When 86 recombinant inbred lines (RILs) derived from crosses between ‘Shumari’ and Acc2265 were grown under these conditions, their flowering dates ranged from the middle of July to the end of October. The distinct bimodal distribution in the RIL population was due to a single major gene, designated Flowering Date1 (FD1). Molecular mapping showed that FD1 was located between the SSR markers Az02‐37M3 and Az02‐40M9, at distances of 6 and 10.4 cM, respectively, on linkage group 2. RILs carrying FD1^S lacked long‐day sensitivity, whereas RILs carrying FD1^A were sensitive to long‐day conditions, confirming that FD1 controls long‐day sensitivity.     

Molecular assessment of genetic diversity in winter barley and its use in breeding

Summary During the last decades extensive progress has been achieved in winter barley breeding with respect to both, yield and resistance to fungal and viral diseases. This progress is mainly due to the efficient use of the genetic diversity present within high yielding adapted cultivars and – with respect to resistance – to the extensive evaluation of genetic resources followed by genetic analyses and introgression of respective genes by sexual recombination. Detailed knowledge on genetic diversity present on the molecular level regarding specific traits as well as on the whole genome level may enhance barley breeding today by facilitating efficient selection of parental lines and marker assisted selection procedures. In the present paper the state of the art with respect to virus diseases, i.e. Barley mild mosaic virus, Barley yellow mosaic virus, and Barley yellow dwarf virus is briefly reviewed and first results on a project aiming on a genome wide estimation of genetic diversity which in combination with data on yield and additional agronomic traits may facilitate the detection of marker trait associations and a more efficient selection of parental genotypes are presented. By field tests of 49 two-rowed and 64 six-rowed winter barley cultivars the genetic gain in yield for the period 1970–2003 was estimated at 54.6 kg ha⁻¹ year⁻¹ (r² = 0.567) for the six-rowed cultivars and at 37.5 kg ha⁻¹ year⁻¹ (r² = 0.621) for the two-rowed cultivars. Analysis of 30 SSRs revealed a non-homogenous allele distribution between two and six-rowed cultivars and changes of allele frequencies in relation to the time of release. By PCoA a separation between two and six-rowed cultivars was observed but no clear cut differentiation in relation to the time of release. In the two-rowed cultivars an increase in genetic diversity (DI) from older to newly released cultivars was detected.     

Variation between genotypes of carnation (Dianthus caryophyllus cultivars and interspecific hybrids) in time of flowering and response to long days. I. Variation in yield distribution

Summary Early flowering carnation cultivars, responding to artificial long days, can assist the grower to plant the onset of flowering and achieve a better distribution of flower production over the year.A comparative trial is described of 20 carnation genotypes (cultivars and backcrosses of interspecific hybrids), representing a wide variation in flowering time and response to long days. The trial was planted in September in a phytotron under a winter light intensity of 15 W/m² for eight hours per day. In one half of the trial, daylength was increased to 24 hours for 25 days in December-January. At the end of February the plants were transferred to a glasshouse where they were observed until all primary shoots had flowered. The main purpose of the experiment was to analyse the genetic factors responsible for the large differences in flowering behaviour between genotypes. Average flowering dates varied from 132 days from pinching in a Dianthus chinensis hybrid to 181 days in the mediterranean cultivar Raggio di Sole. LD response was most pronounced in the earliest flowering Diantini selections and least in the traditional commercial cultivars. In the former the LD effect was evident in all shoots of a plant, but mostly so in the lower (older) shoots; in the traditional cultivars only the higher placed shoots responded to LD. As a result, the proportion of the shoots actually responding to LD varied from 28% in the traditional cultivars to 54% in the Diantini x D. Allwoodii cv Doris group of genotypes.     

A model describing the flowering of single plants, and the heritability of flowering traits of Dimorphotheca pluvialis

In the development of new crops such as Dimorphoteca pluvialis (L.) Moench, improvement of flowering synchronisation is an important breeding objective. The flowering of single plants of Dimorphotheca pluvialis could be described by a logistic curve obtained by the regression of cumulative number of open flowers on time. The curve is characterised by three parameters, corresponding with the total number of flowers produced by the plant, the rate of flowering development and the day at which peak bloom is reached. From these parameters two other characteristics were derived, i.e., onset of flowering and duration of flowering. The use of the flowering model for selection for improved flowering synchronisation is discussed. Heritabilities of flowering traits were estimated using parent-offspring regression and variance components analyses. Onset of flowering and date of peak bloom showed high (>0.69), and total number of flowers moderate to high (0.30–0.90) heritability values, indicating that for these traits considerable progress may be expected from mass selection, particularly in the early selection generations. Duration of flowering showed low to moderate values (0.25–0.45), and methods other than mass selection (e.g. family selection) should be considered. Determination of phenotypic and genetic correlations revealed only an additive genetic correlation between date of peak bloom and duration of flowering (r _A = 0.80 and 0.69 for 1993 and 1994, respectively), suggesting the possibility of indirect selection for curtailed duration of flowering by means of selection against late date of peak bloom. Duration of flowering, total number of flowers and onset of flowering were not correlated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Wheat cellular thermotolerance is related to yield under heat stress

Cellular thermotolerance in terms of cellular membrane thermostability is often implied as an indication of crop heat tolerance and it is therefore considered as a possible selection criterion for heat tolerance. While there is ample genetic variability for cellular thermotolerance in wheat and other crop plants its relations to yield under heat stress is not sufficiently established. This study was performed to assess the genetic relations in wheat between cellular thermotolerance and yield under heat stress. In one study the co-segregation among cellular membrane thermostability (CMS), yield under chronic heat stress and yield under non-stress conditions was evaluated in a random inbred line (RIL) population of a cross between heat resistant (Danbata) and heat susceptible (Nacozari) cultivars. In a second study the same association was evaluated for yield under heat stress in 49 F₇ breeding lines randomly selected from a breeding program. CMS was assayed in growth chamber grown and heat-hardened seedlings. Yield was evaluated under Mediterranean summer irrigated conditions where chronic heat stress caused a reduction in mean yield of the RIL population by 47% as compared with the normal winter growing conditions (non-stress). The RILs varied significantly (p<0.05) for CMS, biomass and yield under stress and non-stress conditions. The two parent cultivars did not differ in biomass or yield under non-stress (winter) conditions but they widely differed for both traits under heat stress. Yield of RILs under heat stress was well distributed between the extreme values of the parent cultivars. There was a significant RIL by season interaction for biomass (F = 9.74; p<0.0001) and yield (F = 10.08; p<0.0001), indicating specific adaptation to heat stress of certain lines in terms of their productivity. Broad-sense heritability for yield was high and nearly the same in the winter (h ²=0.71)and the summer (h ²=0.67). Broad-sense heritability for CMS was high (h ²=0.74). CMS was positively and significantly (p<0.01) correlated across 98 RILs with biomass (r = 0.60* *) and yield (r = 0.53^**) under stress but rot with biomass or yield under non-stress conditions. The 49 breeding lines varied significantly (p<0.01) for CMS and yield under chronic heat stress in the summer season. CMS and yield were significantly correlated (r = 0.56^**) across lines. Overall the associations between CMS and yield under heat stress were reasonably strong and significant but not perfect. Other factors besides cellular thermostability may support yield under heat stress. CMS alone cannot be used as the exclusive selection criterion for heat tolerance in wheat breeding. lt may be valuable as a supplemental criterion in the final breeding stages or as a rough selection tool to reduce a large population into the most likely heat tolerant core at the early stages of the breeding program.     

Quantitative trait loci for fruit size and flowering time-related traits under domestication and diversifying selection in cucumber (Cucumis sativus)

In cucumber, the genetic basis of traits under domestication and/or diversifying selection is not well understood. Here, we reported QTL mapping for flowering time and fruit size-related traits with segregating populations derived from a cultivated × wild cross. Phenotypic data of flowering time (FT), fruit size (FS), fruit number (FN) and fruit weight per plant (FW) were collected in multiple environments. QTL analysis identified 19 QTL for these traits. We found that the major-effect QTL FT1.1 played an important role in regulating flowering time in cultivated cucumber, whereas the minor-effect QTL FT6.3 contributed to photoperiod sensitive flowering time during domestication. Two novel consensus FS QTL, FS1.4 and FS2.3, seem to be the targets of selection during breeding for the US processing cucumber. All other FS QTL were co-localized with previously detected QTL using populations derived from cultivated cucumbers, suggesting that they were under selection during both initial domestication and subsequent improvement. Results from this study also suggested that the wild cucumber is a useful resource for capturing positive transgressive segregation and novel alleles that could be explored in cucumber breeding.     

Studies on the reproductive biology of white yam (Dioscorea rotundata Poir.)

Summary Investigations were conducted on the identification and distribution of yam natural pollinators, flowering pattern and hybridization of white yam (Dioscorea rotundata Poir.) at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, in order to provide informations for producing hybrid seeds needed for vam genetic improvement.Insects belonging to the Coleoptera (48.0%), Diptera (20.4%), Hymenoptera (20.0%), Hemiptera (5.8%), and Thysanoptera (5.8%) were caught around yam plants and presumed to be pollinators: they entered open-receptive-flowers and their presence on yam plants coincided with the duration of the flowering period.Studies on the flowering pattern revealed that: (i) Male and female clones differed in their periods of flower initiation as well as the flowering duration; (ii) Seed production and conventional breeding methods are feasible if staggered planting, water and soil fertility could be managed to ensure that flowering periods of males and females nick and also extend flowering.Artificial pollinations within white yam and between white yam and yellow yam (D. cayenensis Lam) using the camel hair brush method were successful, but resulted in a relatively low fruit set (31.8% maximum). This method was more effective than natural pollination (19.2%) and can thus supplement it for the production of hybrid seeds for introducing genetic variation in yam breeding populations.     

Linkage relationships of genes for leaf morphology and double flowering in Matthiola incana

Summary The inheritance and linkage relationships of a leaf morphology gene of Matthiola incana were investigated. The allele for sinuate leaf shape, c, was found to be recessive to the allele for normal entire leaf, C. The c allele was tightly linked to the recessive allele for double flowering, s. The recombination frequency between the two loci was close to zero. The mode of inheritance of the C gene was in accordance with the hypothesis that a pollen lethal gene is responsible for the constant 1:1 segregation ratio of double-flowered (= male sterile) to single-flowered (= fertile) plants in most M. incana breeding lines. The sinuate leaf allele seemed to reduce the frequency and delay the flowering of double-flowered plants. The importance of the C gene as a double flowering marker in the cultivation and the breeding of M. incana is discussed.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1128-E, 1993 series.     

Bayesian threshold analysis of breeding values,genetic correlation and heritability of flowering intensity in <Emphasis Type="Italic">Eucalyptus cladocalyx</Emphasis> under arid conditions

In the dry regions of Chile, prolific flowering from forest plantation is particularly advantageous for honey production, in order to supplement the erratic flowering in native plants. Eucalyptus cladocalyx is a species suitable for areas with low water availability and their flowers provide a reliable source for the production of honey. The aim of this study was to examine the heritability of flowering intensity in 49 open-pollinated families of E. cladocalyx in southern Atacama Desert, Chile, with the view to the selection for prolific flowering, but with minimal impact on precocious flowering. The Bayesian variance component estimation model was assumed using the Gibbs sampling algorithm. Threshold models were fitted to flowering data (bi-character model). Flowering intensity was found to be highly heritable (posterior mean: h ² = 0.48; and credible interval: 0.41–0.56). The posterior mean of the genetic correlation between flowering precocity and intensity was positive (r = 0.45) and according to the credible interval (0.341–0.542), it was significantly different from zero, indicating that selection on breeding values of early flowering at age three, would have significant and positive impact on flowering intensity 5 years later (or in 8-year-old trees). These results are important for the start of a small-scale breeding program for the species in southern Atacama Desert. The genetic variability found in these breeding populations may be used for breeding purposes in regions where arid environmental conditions are limiting to the establishment of eucalypts trees.     

Genetic variability and heritability estimates for hardseededness and flowering in balansa clover (Trifolium michelianum Savi) populations

Suitability of annual pasture legume species like balansa clover (Trifolium michelianum Savi) in southern Australian farming systems depends on their hardseededness and time to flowering. Late maturing varieties with increased rate of hardseed breakdown, particularly in the late summer—early autumn period are desirable to ensure reliable regeneration in permanent pastures. Two half-sib family balansa clover populations were used to estimate heritability for the rate of breakdown of hardseededness and time to flowering. High narrow-sense heritability estimates (90.5–96.1%, rate of hardseed breakdown; 85.9–94.5%, time to flowering) were obtained, and were mainly attributed to additive gene effects. There was no relationship between rate of hardseed breakdown and time to flowering in Group1 half-sib family, which indicated that selection for both traits could be undertaken independently. In half-sib family Group 2 the relationship between the two traits suggested the possibility of selecting late maturing cultivars with increased rate of hardseed breakdown. Significant differences in time to flowering and rate of hardseed breakdown both within and between the two half-sib family groups suggested that phenotypic recurrent selection would be effective in improving the traits in these populations.     

Effects of irradiance and juvenility on the selection of chrysanthemums

Summary Chrysanthemum morifolium seedlings and cuttings from those seedlings were grown to flowering at 17°C, short days (8 h) and two levels of irradiance (10 and 30 W m^–2). The cuttings flowered more readily than the seedlings at both irradiances, Especially at 10 W m^-2 many seedlings remained vegetative. The delay in flowering of the seedlings was accompanied by a higher number of leaves produced before flowering.The number of leaves produced by the seedling in excess of the number of leaves produced by the cutting from that seedling varied considerably between genotypes. The correlations between seedlings and the corresponding cuttings for days to flowering and number of leaves were low but generally significant.It is concluded that cuttings are preferred over seedlings in breeding programmes that aim at developing chrysanthemums for low light winter production.     

EMS Induction of Early Flowering Mutants in Spring Rape (Brassica napus)

Studies were undertaken to induce early flowering mutants by ethyl methanesulphonate (EMS) treatments of Brassica napus seeds. EMS treatments for 12 h of a highly inbred B. napus line TBS had adverse effects on M¹ plant development and fertility only when concentrations were greater than 1%. However, an EMS concentration of 1.5% did not reduce M₁ plant fertility to an extent which significantly reduced production of M₂ seeds. Genetic changes induced by EMS treatment and affecting flowering time were of three main types: (1) Changes within a polygenic system reflected by increased variation in flowering time among M₂ families. As the increase in variation was due primarily to a higher frequency of later flowering plants, these polygenic changes would be of little value in developing better-adapted cultivars. (2) Induction of a recessive mutation at a major gene locus which caused M₃ plants homozygous for the mutant gene to flower at least 20 days earlier than the parental line TB8. (3) Induction of a dominant mutation at a major gene locus which affects flowering time by causing a substantial reduction in vernalization requirement. M₂ plants carrying the mutant gene flowered as early as 59 days before the parental line. These major gene mutations could be rapidly exploited in the development of agronomically superior cultivars for short-season, lower rainfall environments in Western Australia.     

Geneticanalysis of drought stress response in rapeseed (Brassica campestris and B. Napus). II. Yield improvement and the application of selection indices

Summary The expected improvement in grain yield if selection was made for plant characters measured between flowering and maturity was evaluated in populations of rapeseed (Brassica campestris and B. napus) grown in a droughted environment. Drought was commenced at flowering in each species and measurements were made on plants at the commencement of the drought stress, during the stress treatment and at crop maturity.Substantial genetic and phenotypic variation was observed in yield as well as the different morphophysiological determinants of yield. In B. campestris no single parameter was found to be a suitable alternative selection criterion to yield since the correlated responses in yield if selection was for another character was lower than if selection was for yield alone. By the use of a selection index however, joint selection for yield, as well as harvest index, 1000 seed weight and seeds per pod, was expected to be 20% more effective than direct selection for yield under drought. In the B. napus population direct selection for flowering time or for harvest index was predicted to result in a genetic advance in yield equal to or greater than that obtained by direct selection for yield, whereas joint selection for flowering time and yield should result in a 16% greater yield increase. Selection for increased yield in these populations grown in droughted conditions is discussed.     

Should spring wheat breeding for organically managed systems be conducted on organically managed land?

Organic spring wheat (Triticum aestivum L.) producers in the northern Great Plains use cultivars which have been bred for conventional management systems or heritage cultivars released before the widespread use of synthetic fertilizers and pesticides. To investigate the feasibility of organic wheat breeding and to determine common genetic parameters for each system, we used a random population of 79 F₆-derived recombinant inbred sister lines from a cross between the Canadian hard red spring wheat cultivar AC Barrie and the CIMMYT derived cultivar Attila. The population, including the parents, was grown on conventionally and organically managed land for 3 years. Heritability estimates differed between systems for 6 of the 14 traits measured, including spikes m⁻², plant height, test weight, 1,000 kernel weight, grain protein, and days to anthesis. Direct selection in each management system (10% selection intensity) resulted in 50% or fewer lines selected in common for nine traits, including grain yield, grain protein, spikes m⁻², and grain fill duration. The results of this study suggest that indirect selection (in conventionally managed trials) of spring wheat destined for organically managed production would not result in the advance of the best possible lines in a breeding program. This implies that breeding spring wheat specific to organic agriculture should be conducted on organically managed land.     

Structure and variation of subterranean clover populations from Sicily,Italy

Summary A collection of subterranean clover lines singled out from populations of the species Trifolium brachycalycinum and T. subterraneum collected in Sicily, Italy, was examined at two localities for flowering time and at one locality for oestrogen content and seed yield. The structure and variation of the populations of the two species were compared. The relationship between flowering time of the populations and some environmental features of their collection sites was examined to assess whether the maturity requirements of the two species were similar and to frame selection models focused on developing varieties of appropriate maturity. Populations of T. subterraneum were, on average, more complex than those of T. brachycalycinum, being characterized by higher number of lines per population and greater intra-population variation for flowering time, oestrogen content and seed yield. Furthermore, populations of T. subterraneum were, on average, about 15 days earlier than sympatric populations of T. brachycalycinum. Both the greater variation and the relative earliness of T. subterraneum occurred irrespective of the environments of origin of the populations. Inferences are drawn on the adaptive advantages that such features confer to T. subterraneum. Mean flowering time of the populations increased on increasing annual rainfall and altitude of the collection sites. However, the changes in maturity appeared almost exclusively related to variations in rainfall in T. subterraneum, while in T. brachycalycinum the effect of altitude was greater and that of rainfall less marked than in the former species.     

The differential responses of chrysanthemum cultivars to light and temperature

Summary Chysanthemum cultivars were grown in 4 experiments in the greenhouse and in the phytotron. The growing conditions in the greenhouse varied from 14 C, 60 J cm² day^-1 to 17 C. 431 J cm² day^-1, those in the phytotron from 12 to 455 J cm^-2 day^-1 at a temperature of either 14 or 20 C.Most cultivars responded differentially to light and/or temperature, but this was only measurable when large differences in light and/or temperature were imposed. Reducing the light level in a greenhouse by 50% does not bring out cultivar×light interactions. Such interactions may be pronounced however when the performance in summer is compared with that in winter. This is also reflected in the correlation coefficients. The correlations between summer and winter performance for number of flowers per stem and the number of days to flowering are non-significant, those for the 7 other traits measured were all significant.The occurrence of interactions does not preclude the possibility of breeding cultivars adapted to a wide range of light and temperature conditions. Appropriate selection procedures are discussed.     

Estimates of genetic variability and heritability for vegetative and reproductive characters of kiwifruit (Actinidia deliciosa)

The results of this study indicated a great deal of genetic variation in a number of characters of horticultural interest in kiwifruit seedling populations, and therefore, a potential to improve kiwifruit by vine selection. High narrow sense heritability was shown for pedicel length(0.62) and flowering duration (0.50) in male vines, and pedicel length (0.67),floral shoot percentage (0.54), leaf length-width ratio (0.64), fruit elongation (0.64) and fruit weight (0.52) in female vines. For these traits, selection of superior seedlings should lead to rapid genetic improvement in these populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic Variability for Mineral Concentration in the Forage of Jerusalem Artichoke Cultivars

Summary One of the potential uses of Jerusalem artichoke (Helianthus tuberosus L.) is as a forage crop. Information on inherent differences in forage nutritional quality is essential if the quality of the forage is to be improved through breeding. The objectives of this study were to determine the genotypic variability among and within forage of Jerusalem artichoke cultivars for the concentration of N, P, Ca, Mg, K and the Ca/P ratio at flowering, to determine if selection among and within cultivars is feasible, to estimate the magnitude of the genotype × environment interaction, and to examine the relationships among mineral concentrations in the forage. Ten cultivated Jerusalem artichoke cultivars grown in an irrigated field nursery at Bushland, TX were evaluated for N, P, Ca, Mg, K, and the Ca/P ratio in the forage at flowering over a 2-yr period. Cultivars, cultivar × year, and error variances were estimated to calculate the phenotypic variance. Estimates of the within-population variances were also determined. The adequacy of Jerusalem artichoke forage at flowering for maintenance of a ruminant animal was classified as follows: N, Ca, Mg, K as adequate, P inadequate, and the Ca/P ratio as excessive. There were genotypic differences among the ten cultivars for N, P, Ca, Mg, K, and the Ca/P ratio for both years and averaged across years. The magnitude of the genotypic variance components indicated that a substantial proportion of the total variation for these elements was due to cultivar, indicating the possibility of improving these elements. However, further studies on heritability and response to selection will be required before conclusions can be reached concerning the likelihood of successfully breeding for these traits.     

Induction of male flowering in gynoecious cucumbers (Cucumis sativus L.) by silver ions

Summary Silvernitrate (AgNO₃) and silverthiosulphate (Ag(S₂O₃)₂ ^3-) effectively induced male flowering in many nodes of 7 gynoecious cucumber genotypes in 3 glasshouse trials. A single spraying of the plants in the first true leaf stage with 3 mM Ag⁺ as Ag(S₂O₃)₂ ^3- or AgNO₃ (500 ppm) yielded many more staminate flowers than GA-3 (1500 ppm) and almost as many as 3 consecutive sprayings of GA-4/7 (50 ppm).Male flowering started about 3 weeks after treatment and lasted for a period of up to 4 weeks thereafter. Plants treated with silver ions did not elongate and grew normally; effective concentrations of AgNO₃ proved phytotoxic only in poor growing conditions, while Ag(S₂O₃)₂ ^3- never gave deleterious side-effects. Even very strongly female lines can be induced to male flowering with silver ions, thus increasing the feasibility of large scale seed production of gynoecious × gynoecious cucumber hybrids.