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  • Author or Editor: Martha A. Mutschler x
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Abstract

Segregating populations from crosses of ‘Alcobaca’ with normal cultivars indicated that storability of the fruit is controlled by a single recessive gene, alc (alcobaca). ‘Alcobaca’ also is homozygous for single recessive genes controlling fruit skin color and leaf morphology, resembling the y and c or e mutants, respectively. ‘Alcobaca’ also possessed altered flower-cluster morphology; however, none of these 3 traits was controlled by or linked to the alc locus. Linkage studies indicate that the alc gene is located near the end of the short arm of chromosome 10, about 20 map units from u (uniform ripening) and 14 map units from hy (homogeneous yellow). The alc locus is therefore about 17 map units from nor (nonripening). This locus increases known, total genetic length of chromosome 10 to 141 units. In allelism tests with nor, detached, mature-green F1 fruit ripen and turn red, unlike the nor and alc parents. This complementary gene action demonstrates the nonallelism of alc and nor. Recombinant plants also were obtained from the F2 of the cross alc × nor, confirming that alc is at a separate locus from nor.

Open Access

Abstract

Storability, ripening, and fruit characteristics were studied in fruit of tomato (Lycopersicon esculentum Mill.) from plants heterozygous or homozygous for alc. Ripe fruit from heterozygotes showed a 78% increase in storability compared to ‘Rutgers’. Full ripe fruit of the homozygous recessive showed over 300% increase in storability, with a mean storage life of 40 days. Increased storability is not associated with initial fruit Firmness, but is accompanied by a decrease in the rate of fruit softening during storage of the fully ripe fruit. This trait does not affect pH, soluble solids, or the time required for development from flowering to mature-green fruit. The rate of further ripening is decreased. The degree of ripeness obtained by the mutant fruit is dependent on its ripeness when the fruit is picked. Mutant fruit will not fully ripen off the vine unless picked when the fruit is already at the late streak to light color stage. Ethylene production is reduced in detached, mature-green ‘Alcobaca’ fruit to 25% of that observed in ‘Rutgers’. A climacteric pattern of ethylene and CO2 production was not observed in single, detached fruit of ‘Alcobaca’ or other alc lines. The highest ethylene production detected externally was observed in the first (day one) reading of alc fruit, regardless of maturity of fruit when picked. Afterwards, ethylene production decreased to 2.5 to 3 μl·kg−1hr−1. The stage of ripeness at harvest affects the level of ethylene production of detached fruit. The maximum day-one ethylene readings were obtained from fruit harvested at the turning (40% color) stage. The rise in ethylene production during ripening also was detected in internal gas samples.

Open Access

Sixteen tomato [Solanum lycopersicum L. (syn. Lycopersicon esculentum Mill.)] genotypes (inbred lines or hybrids) were tested against five Phytophthora infestans (Mont.) deBary isolates to characterize race specificity of late blight resistance transferred to tomato from Solanum pimpinellifolium L. [syn. Lycopersicon pimpinellifolium (L.) Mill.] accession L3708. The effects of plant genotype, isolate, genotype × isolate, and isolate × replication interactions were highly significant (P = 0.001). Set of four sister lines fixed for late blight resistance (CU-R lines) exhibited full and equal resistance to the five pathogen isolates tested. In contrast, the heterozygous F1 hybrids, created by crossing the resistant CU-R lines with a susceptible parent, were resistant to US-11; partially resistant to US-17, NC-1, and DR4B; and susceptible to US-7. Differential responses were also observed across pathogen isolates on a set of resistant sister lines (CLN-R lines), which also were bred from L3708. The CLN-R lines were resistant to the DR4B, NC-1, and US-11 isolates, but showed significant disease-affected areas and sporangium numbers following inoculation with either US-7 or US-17. Restriction fragment length polymorphism (RFLP) analysis confirms that both CU-R and CLN-R are homozygous for the Ph-3 gene derived from L3708. Since progeny tests also confirmed that the CLN-R lines are fixed for their level of resistance, these results suggest that late blight resistance in the CU-R lines is not controlled by Ph-3 alone, and that at least one additional gene conferring late blight resistance is missing from the CLN-R lines. Results of genetic tests of the (CU-R × CLN-R) F1 and a (CU-R × CLN-R) F2 population with the pathogen isolate US-17 strongly support a model in which resistance of the CU-R lines requires genes in addition to Ph-3. The implications of this information in breeding for late blight resistance and using of the resulting resistant lines or hybrids are discussed.

Free access

Late blight [caused by Phytophthora infestans (Mont.) de Bary] causes severe loss of tomato [Solanum lycopersicum L. (formerly Lycopersicon esculentum Mill.)] production in environments favorable to the pathogen. Researchers at the Asia Vegetable Research Development Center (AVRDC) identified resistance to late blight in an accession of S. pimpinellifolium [formerly L. pimpinellifolium (L.) Mill.] that they named accession L3708. This resistance has now been transferred to processing tomato lines, which are resistant to multiple P. infestans isolates. Lab trials, inoculated field trials in New York, and naturally infested field trials in Mexico all indicate that these processing tomato lines are fixed for late blight resistance. Segregation data obtained for resistance in the breeding populations were dependent on the pathogen isolate used for the disease screen. Segregation data do not support the hypothesis of single gene control of the full resistance trait, but instead suggest that more than one gene is involved, and that these genes interact in an epistatic manner.

Free access

Abstract

Pollen tube growth and ovule fertilization was observed in 3- to 7-mm-long pistils in flowers of a rapid cycling population of Brassica campestris L. Pollen tubes grew past the ovules to the base of the ovaries in pistils 3- or 4-mm-long. The pollen tubes were guided toward the ovules in buds 5-mm-long or longer and in flowers of compatible or incompatible plants. Brightly florescent spots were observed at the micropyle of ovules in pistils 4-mm or longer, but not in smaller buds.

Open Access

The transfer of multigenic traits into tomato has been slow due to interspecific barriers (hybrid breakdown) found in the F2 of the Lycopersicon esculentum × L. pennellii cross (esc × pen), including blocks in normal reproductive development and nonfecundity. In a typical (esc × pen) F2 population, failure to flower and premeiotic blocks in pollen development occurred in 2% and 11% of the population, respectively. The remaining plants showed a mean of 37% stainable pollen. Twenty three percent of the F2 plants set seed, with an average of 4.5 seeds/fruit. An average of 33% of the stainable pollen from the 7 F2 plants with the highest stainable pollen measurements germinated in vitro, but only 4 of these 7 plants set seed. Thus, percent stainable pollen is not an adequate predictor of fecundity, and the non-fecundity in the F2Le plants must involve barriers occurring after pollen germination.

A method was developed which greatly reduces or eliminates each of the F2 barriers. The method and its efficacy on each of the aspects of hybrid breakdown will be discussed.

Free access

Little is known about the mechanisms controlling interspecific barriers, unlike the well studied intraspecific barrier, self incompatibility (SI),. A unilateral crossing barrier (unilateral incongruity - UI) exists among the Lycopersicon species, in which crossing is impeded or prevented in one direction. Since both UI and SI can give unilateral differences in seed set, suggestions have been made that UI and SI are functionally related. L. pennellii LA716 is self-compatible, unlike the other accessions which are SI, but LA716 still exhibits UI with L. esculentum (esc). We observed the development of pollen tubes in self and cross pollinations of LA716, esc and SI accessions of L. pennellii (pen). Selfed pollen tubes in esc were at the ovary in 24 hours, while pen were 1/2 way down the style and in LA716 the pollen had not germinated. By 48 hours, the pollen tubes in LA716 were in the ovary and growth had halted in pen styles. Crosses with LA716 pollen on esc and pen resulted in pollen tube growth starting within 24 hours continuing to the ovary. Thus, UI is not a SI response and LA716 shows a delayed pollen germination and growth unlike the other Lycopersicon species examined.

Free access

Abstract

One of the most popular types of winter squash is the butternut squash, a member of the species Curcurbita moschata Duchesne. Butternut squash has a buff-colored exterior and deep orange-colored flesh. Although winter squash of this species were cultivated before colonial times, the typical butternut fruit shape is a recent innovation. Crookneck (CR) types were widely used in the temperate United States until the origin in the early 1930s of the shortnecked butternut (BN) fruit type from a crookneck cultivar. The unstable nature of the butternut trait was soon noted, but could not be explained. The purpose of this paper is to summarize published and unpublished information concerning the origin, characteristics, and genetic behavior of the buttemut/crookneck fruit trait.

Open Access