Department Plant Science, University of New Hampshire Durham, NH, 03824
We have identified a gene in tomato associated with wilting. Several recessive mutations described previously cause wilty phenotypes: impatiens (imp), notabilis (not), flacca (flc), and sitiens (sit) ( Jones et al, 1987; Mutschler and Rick, 1987). Not, flc, and sit have been mapped and characterized. All three reduce abscisic acid production, resulting in impaired stomatal function and loss of turgor (Neill and Horgan, 1985).
The new wilty mutation was discovered in 'Large Plum', a presumed land race of Italian origin, which we received from Johnny's Selected Seeds in Albion, Maine. 'Large Plum' is slow-growing, indeterminate, and produces plum-type fruit. Mature plants are large and viney. All plant parts are somewhat elongated relative to normal cultivars: internodes, leaves, leaflets, floral parts and fruit. 'Large Plum' wilts in typical field and greenhouse conditions where other cultivars maintain turgor. Wilting is apparent throughout plant development. Drooping of the leaves is moderate to severe, depending on atmospheric conditions, and is not relieved by watering. Plants survive to maturity and produce fruit, despite reductions in turgor. In the greenhouse,'Large Plum' also exhibits progressive leaf marginal necrosis beginning at the four-leaf stage or sooner. As plants develop, necrosis progresses inward, consuming the leaves. Older leaves succumb first, and leaf death proceeds up the plant.
We determined that the wilty mutation was inherited as a single dominant gene, based on segregation analysis of F2 populations from crosses between 'Large Plum' and normal (non-wilty) cultivars (Table 1). All F1 individuals from these crosses were wilty. Crosses between 'Large Plum' and recessive wilty mutant stocks carrying imp, not, flc, and sit, revealed lack of allelism between the dominant wilty gene and all of these mutations (Table 2). F1 plants from all crosses were wilty; therefore wild type plants in F2 populations were recorded as evidence of complementation.
Table 1. F1 phenotype and F2 segregation analysis of progeny derived from crosses between 'Large Plum' (wilty ) and normal cultivars.
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Cross F1 F2 observed F22 expected P
wilty normal wilty normal
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Coldset x Large Plum wilty 47 13 45 15 .5 <P> .7
Large Plum x Coldset wilty 44 16 45 15 .75 <P> .9
Nova x Large Plum wilty 42 18 45 15 .3 <P> .5
Large Plum x Nova wilty 93 27 90 30 .5 <P> .7
Pink Girl x Large Plum wilty 102 42 108 36 .2 <P> .3
Large Plum x Pink Girl wilty 50 10 45 15 .1 <P> .2
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Table 2. Results of tests for allelism in F2 populations of crosses between
'Large Plum' dominant wilty and four recessive wilty mutations.
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Cross Phenotypic Classes Test ratio P
Wlt/+ +/+ Wlt/mut +/mut
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Wlt x flc 51 15 34* 9:3:4 .10 < P > .20
Wlt x sit 59 24 17* 9:3:4 .10 < P > .20
Wlt x imp 51 21 22 8 9:3:3:1 .50 < P > .70
Wlt x not 54 23 18 5 9:3:3:1 .75 < P > .90
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*Wlt / mut and + / mut phenotypes were indistinguishable due to the severity
of sitiens and flacca mutations.We conclude that 'Large Plum' carries a unique mutation associated with wilting, and propose the gene designation Wlt to represent this mutation. The mutation may be useful for investigations of the genetic basis for turgor maintenance and drought stress physiology. 'Large Plum' seed is being supplied to the Tomato Genetic Resource Center at the University of California, Davis, CA.
References:
Jones, H. G., C. S. Sharp, and K. H. Higgs. 1987. Growth and water relations of wilty mutants of tomato (Lycopersicon esculentum Mill.). J. Exp. Bot. 38 (196): 1844-1856.
Mutschler, M. A., and C. M. Rick. 1987. Linkage maps of the tomato. Report of the Tomato Genetics Cooperative 37: 5-31.
Neill, S. J. and R. Horgan. 1985. Abscisic acid production and water relations in wilty tomato mutants subjected to water deficiency. J. Exp. Bot. 36 (169): 1222 - 1231.