Search Results
Abstract
‘O roblanco’ is an early-maturing, seedless grapefruit-type citrus released for use in the interior areas of California. It may be suitable for interm ediate climate zones in other citrus areas. Fruit quality has not been satisfactory in cool, humid climates nor in hot desert areas.
Abstract
The percents of polyembryonic seeds of 65 tetraploid Citrus hybrids and 33 related, probable tetraploids were scored. These plants arose from crosses of 2 diploid, sexual, monoembryonic cultivars by a total of 6 tetraploid, partly asexual, polyembryonic pollen parents. Plants classed as strictly monoembryonic were recovered in progenies from 3 of the tetraploid parents. Individuals with low percentages of polyembryonic seeds were obtained in all progenies. The likelihood that 1 or 2 genes are responsible for polyembryony is discussed.
Abstract
‘Melogold’ is an early-maturing, seedless, hybrid grapefruit-type citrus released for use in interior areas of California. It may be suitable for intermediate climate zones in other citrus areas. Fruit quality has not been satisfactory in cool, humid climates nor in hot desert areas.
Abstract
C35 and C32 citranges are being released for rootstock trial because of their relative tolerance to the citrus nematode (Tylenchulus semipenetrans Cobb), to Phytophthora species, and to the tristeza virus. They also impart considerable vigor to their scions and have shown satisfactory yields with some scions in limited tests. Each has certain characteristics that could limit its use.
Abstract
In 5 separate field-planted groups at 2 climatic locations, F1 populations and 3-way crosses involving pummelo as an immediate parent have all shown significantly larger mean trunk size, and generally larger canopy size, than crosses which lack pummelo. The other parents included oranges, mandarins, tangors (tangerine × orange), grapefruit, and the related genus Poncirus. F2 progenies and backcrosses to non-pummelo cultivars showed less vigor than the compared F1’s. Fruiting has occurred earlier and in higher proportions of trees among the pummelo crosses with Poncirus, and often with the other pummelo hybrids. These characteristics seem to represent hybrid vigor based on favorable combining ability of the pummelo, although only a limited number of pummelo cultivars were tested. The species appears to be relatively homogenous, and is one of the few Citrus species which reproduce entirely by sexual embryony. The behavior of its hybrids supports the concept that pummelos carry fewer unfavorable genes, and may be more homozygous, than Citrus species and cultivars which reproduce largely by asexual embryony.
Abstract
The degree of multifoliolate leaf expression in 272 F1 hybrid and 132 first backcross field trees involving unifoliolate Citrus and trifoliolate Poncirus is reported. Among the F1's of 9 Citrus cultivars × Poncirus, 246 trees had >50% multifoliolate leaves and only 7 had 30% or less. Individual crosses all showed similar behavior. Among the backcrosses to Citrus, 23 trees had >30% multifoliolate leaves and 109 had 30% or less. No multifoliolate leaves were observed in 55 of these. Environment had a discernible, but not a major, effect on leaf type. The data imply that only a few genes control leaf type in these crosses but the exact genetic basis is uncertain.
Abstract
High proportions of 3x hybrids were obtained from crosses of 4x highly sexual seed parents by 2x pollen parents in Citrus. This is in contrast to the low proportions usually obtained with 4x partly apomictic cultivars as seed parents, or with 4x plants used as pollen parents. Initial survival of small germinating seeds and very young seedlings was low but later growth vigor has been high. Ten 4x and 9 aneuploid (near 3x) plants were identified.
Abstract
Fourteen hybrid citrus progenies having polyembryonic Poncirus as a parent or grandparent were classified for their type of embryony, by seed dissection. Seedling populations from some of the hybrids were also studied. The ratio of polyembryonic (P) to monoembryonic (M) individuals was nearly 1:1 among 52 F1 hybrids from P Citrus × P Poncirus. The ratio was about 1 P to 6 M among 121 F1's from 5 crosses of M Citrus with P Poncirus. Among 15 individuals from a backcross of Citrus × (Citrus × Poncirus) which was M × P, only 2 were clearly P. From backcrosses of M × M(?) parents, 28 individuals were M, 3 were probably M, and only 1 (a possible outcross?) was P. Results from the P × P and P × M crosses are in contrast to those from similar types of crosses within Citrus, where much higher proportions of P hybrids have usually been found. Results from the M × M(?) crosses probably support the concept that crosses between monoembryonic strictly sexual taxa produce only monoembryonic sexual progeny. A genetic basis for the inheritance patterns is discussed.
Abstract
Tomato (Lycopersicon esculentum Mill.) accession PI 270248 (‘Sugar’) had high levels of resistance to bacterial spot [incited by Xanthomonas campestris pv. vesicatoria (Doidge) Dye] on fruit, but foliage was susceptible. Hawaii 7998 (H7998) was highly resistant to foliar infection, but was intermediate in resistance to fruit infection. Fruit spot on hybrids between ‘Sugar’ and H7998 was usually intermediate to the parents. Occasionally, disease incidence of hybrids was not statistically different from one or both parents, but tended to resemble ‘Sugar’ more closely than H7998. There were no significant differences between reciprocal hybrids, indicating a lack of cytoplasmic inheritance. Under low disease incidence, hybrids between ‘Sugar’ and ‘Walter’ (susceptible to bacterial spot on fruit and foliage) had fruit spot incidence similar to ‘Sugar’ and significantly less than ‘Walter’. Thus, there was a high level of dominance for resistance to bacterial spot on fruit.
A `spray-inoculation seedling screening procedure was developed for detecting resistance to Xanthomonas campestris pv. vesicatoria (Doidge) Dye, causal agent of bacterial spot of tomato (Lycopersicon esculentum Mill.). Two-week-old transplants were preconditioned under 95% humidity for 16 hours before spray inoculation and then rated for bacterial spot 2 weeks later. Resistant plants could also be distinguished from susceptible genotypes using a modified bacterial speck [Pseudomonas syringae pv. tomato (Okabe) Young, Dye, and Wilkie] screening procedure (cotyledon-dip technique). When results of both screening methods were compared to field ratings from three previous seasons, significant correlations were more frequently observed for the spray-inoculation method. In Summer 1991, individual plants were evaluated by the spray-inoculation technique and then were placed in the field to determine susceptibility under field conditions. Correlations (r = 0.28 to 0.34) between spray-inoculation seedling screening ratings and field ratings, although low, were significant (P ≤ 0.0001). More than 90% of susceptible plants could be eliminated, saving labor, space, and time.