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Abstract
The inheritance and linkage relationships among isocitrate dehydrogenase, phosphogluconate dehydrogenase, and peptidase with phenyl-alanyl-proline were determined. Progeny segregations fit a model for a dimeric enzyme encoded by one disomic locus with two alleles. Linkage associations among the three loci were not detectable with recombination fractions ranging between 0.353 to 0.481 among these loci.
Plant improvement incorporating quantitatively inherited yield component traits is technically difficult, time consuming, and resource demanding. In melon (Cucumis melo L.), the inheritance of yield components is poorly understood. A unique highly branched fractal melon plant type has been developed by the U.S. Department of Agriculture (USDA) from exotic germplasm to improve yield of U.S. Western Shipping type melons (Group Cantalupensis). In order to more effectively develop useful germplasm for commercial use the genetic of components of yield must be clearly understood. Thus, the genetics of branching, an important yield component, was investigated. Melon progeny derived (F1, F2, F3, BC1P1, and BC1P2) derived from a cross between USDA line 846-1 (P1) and Top-Mark (P2) were used to evaluated in two locations (Wisconsin and California) to estimate of components of variance, and narrow-sense (h2N) and broad-sense (h2B) sense heritabilities. Lateral branch numbers among 71 to 119 F3 families were significantly different (P ¾ 0.01) regardless of test environment. Covariance analyses indicates that branching is moderately heritable (h2B = 0.62 to 0.76, h2N = 0.43 to 0.48), and conditioned by several additive factors (perhaps 2 to 4) that are highly additive. Although environment plays an important role in lateral branch development, family rankings over environments were relatively consistent, indicating that effective selection for this trait should be useful for incorporating the fractal plant habit into Western Shipping melon. The significant additive component underlying lateral branch number indicates that quantitative trait loci (QTL) conditioning this yield component might be identified for use in marker-assisted selection.
A study was designed to determine whether temperature alone or temperature and relative humidity (RH) interactions affect the development of pillowy fruit disorder (PFD) in cucumber (Cucumis sativus L.). Fruit of `Calypso', `Flurry', `Carolina'? and inbred breeding line 39 were matured in four environments: cyclic and high (22 to 45C) and moderate (22 to 30C) temperatures at two RHs (35% and 75%). PFD symptoms were most severe at high temperature and RH; thus, both contribute to the development of this disorder. Line 39 had the highest PFD ratings, regardless of growing environment, a result indicating that cultigens respond differently to these imposed stresses.
Chilling damage can cause major reductions in cucumber (Cucumis sativus L.) yield. Cucumber plants can withstand a chilling event (i.e., tolerance and susceptibility), in which response is dictated primarily by maternally inherited plastid genomes or by the biparental contribution of a nuclear factor. To examine the modes of inheritance, exact reciprocal backcross cucumber populations (BC1–5), were created by crossing ‘Chipper’ (chilling-tolerant plastid, susceptible nucleus) and line North Carolina State University (NCSU) M29 (chilling-susceptible plastid, susceptible nucleus). These progeny and their parents were subjected to chilling stress [5.5 h at 4 °C in 270 μmol·m−2·s−1 photosynthetic photon flux (PPF) cool white lighting] at the first true-leaf stage. The chilling response of individuals possessing either NCSU M29 or ‘Chipper’ cytoplasm in any generational comparison was not significantly different (P > 0.05) from that of the maternal plastid source (susceptible or tolerant). Moreover, lines within a plastid type did not differ significantly (P > 0.05) in chilling response despite unequal nuclear contributions demonstrating the absence of nuclear additive or dosage effects originating in ‘Chipper’ or NCSU M29. Additionally, line NC-76, previously identified as a nuclear source of chilling tolerance, performed intermediate to ‘Chipper’ and NCSU M29 in chilling response under these stress conditions. The F1 progeny derived from crossing both BC5 plastidic response types (susceptible and tolerant) with NC-76 (paternal parent) performed comparable to their plastid donors and were significantly different (P < 0.0001) from one another despite their heterozygous nuclear nature resulting from the contribution of the nuclear chilling-tolerant factor contributed by NC-76. The response of tolerant and susceptible BC5 lines (i.e., ‘Chipper’ plastid in the NCSU M29 background and NCSU M29 plastid in ‘Chipper’ background, respectively) was reversible by crossing BC progeny with an alternate chilling-response plastid type. It is concluded that under these chilling conditions, plastid effects determine tolerance or susceptibility in the cucumber germplasms examined.
Two experiments (1989 and 1990) were designed to characterize the response of cucumber (Cucumis sativus L.) plants with different leaf types [normal leaf (LL) vs. little leaf (ll)] to high soil moisture tension (SMT) and to determine whether hydrocooling would reduce the severity of pillowy fruit disorder (PFD). Comparisons were made among nine cultivars (7 LL and 2 ll) for aboveground vegetative and fruit response, and between two irrigation regimes. High SMT generally caused increased wilt ratings and stomatal conductance and decreased plant dry weight. PFD severity of fruit from watered plots was less [61% (Expt. 1, 1989) and 26% (Expt. 1, 1990)] than of fruit harvested from plots in which water was withheld. The response of the two ll cultivars to moisture stress differed depending on environmental conditions. Increased PFD severity was associated with increased temperature, lower relative humidity (RH), and excluding hydrocooling during postharvest handling. Of the four storage treatments examined, hydrocooling to ≈8.5C then storage at 15C and 85% RH for 4 days produced fruit with the least PFD symptoms. Fruit of `Carolina' (LL) exhibited the highest PFD ratings, while those of `Calypso' (LL) were consistently low compared to other cultivars. Processors can lower PFD incidence and severity by ensuring that adequate moisture is available to plants during fruit enlargement and that harvested fruit are hydrocooled before shipping and storage.
Mean daily stomatal resistance was higher (58%; to 384%), photosynthesis values lower (11% to 49%), and crop water stress index values higher (92% to 95%) in stressed cucumber (Cucumis sativus L.) plants than in irrigated control plants in three experiments performed in 1987 and four in 1988. Pillowy fruit disorder (PFD) was more frequent (110% to 150%) and more severe (59% to 81%) in freshly harvested fruits from stress plots when compared to controls. No after-storage differences in PFD were detectable between water stress treatments. Mean PFD ratings of processed fruit following postharvest storage at 26.5C and either 60% or 75% relative humidity were significantly higher than ratings of fruit stored at either 10.5 or 15.5C and 85% relative humidity. The progressive development of pillowy and the observed enhancement of PFD symptoms following storage at higher storage temperatures indicated that postharvest changes can occur in fruit mesocarp tissue and that the development of PFD can be altered, to some extent, during storage. Negative correlations (- 0.18 to - 0.78) between fruit quality and PFD ratings suggested that these changes can affect processed product quality. Pillowed tissue of processed fruit was significantly softer (33% to 39%) than nonpillowed tissue.
Four cucumber (Cucumus sativus L.) inbred lines were intermated then bulked maternally to create four base populations denoted as cycle 0 (i.e., Pop.1 C0, Pop.2 C0, Pop.3 C0, Pop.4 C0). Each of these populations underwent phenotypic selection (PHE; open-field evaluations), selection by marker (MAS; genotyping at 20 marker loci), and random mating (RAN; no selection) for three cycles. The four traits under selection, multiple lateral branching (MLB), gynoecious sex expression (GYN), earliness (EAR), and fruit length to diameter ratio (L:D), are quantitatively inherited, controlled by relatively few (two to six) QTL per trait and are directly related to yield. Using the same C0 populations and selection scheme allowed a direct comparison of the effectiveness of MAS and PHE. Because each C0 population varied for any given trait, the response to MAS and PHE was not the same for each population. In general, C0 populations that were inferior for a trait either responded favorably to selection or remained constant, while those with superior trait values either did not change or decreased. Both MAS and PHE provided improvements in all traits under selection in at least one population, with the exception of MAS for EAR. MAS and PHE were equally effective at improving MLB and L:D, but PHE was generally more effective than MAS for GYN and EAR. When considering all traits, responses to PHE were superior in three of the four populations. The population for which MAS was superior, however, showed the only increase in yield (fruit per plant), which was not under direct selection. These results indicate that both MAS and PHE are useful for multi-trait improvement in cucumber, but their effectiveness depends on the traits and populations under selection.
During winter months, a substantial volume of various horticultural products are imported to the United States from the Caribbean and Central and South America. United States cucumber (Cucumis sativus L.) processors who market fresh-pack and refrigerated products require raw product daily to meet consumer demands. Mexico serves as a single-source supplier to all United States processors during this period, and thus Mexican production represents certain price risks. United States processors would consider other growing regions to reduce these risks if financially attractive alternatives could be identified. Therefore, a project was initiated to acquire information on production and export costs in Hispaniola (Dominican Republic and Haiti), and to compare those to Mexican and United States production and transport costs. Experimentation lead to the identification of the critical influences of market prices, costs and conditions for the financial feasibility of establishing a processing cucumber industry on Hispaniola. Comparative evaluation indicated that significant variation in total cost was caused by fluctuations in transport, tariffs, and labor cost components. The causes of variation in transportation costs were distance, method (sea, air, truck), competitive demand (volume), and shipping frequency, consistency, and capacity.