Title | Embryo callus hybrids |
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Abstract |
Not available – first paragraph follows:
Hybridization between cultivated species and related wild species has been of great value for cultivar improvement. Genes that enhance the survival of the wild species by providing disease or insect resistance, salt tolerance, cold tolerance, and the like, often confer the same trait on the cultivar to which they are transferred. Fertility barriers restrict the number of wild species that can contribute genes to any particular cultivated species through normal sexual crosses, but these fertility barriers can often be overcome through the use of special procedures. |
Authors |
Pratt, David : David Pratt, Professor, Bacteriology, U.C., Davis.
Thomas, Bruce R. : Bruce R. Thomas, formerly graduate student, U.C., Davis.
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Publication Date | Aug 1, 1982 |
Date Added | Jul 17, 2009 |
Copyright | © The Regents of the University of California |
Copyright Year | 1982 |
OCR Text |
to suboptimaltemperatures is among the neg - Scanning electron micrograph of pollen grain germinating lected areas of potentiallyuseful research and of stigma . on surface development . Sensitivityto chilling in many important crop plants limits their climatic distribution for economic production . Even in areas normally suited to these crops , this sensitivity causes losses through injury suf - fered from sporadic low temperatures . Our laboratory has been exploiting the ex - isting genetic diversity in wild tomato germ - plasm forplant breeding to reducecrop losses and allow expansion into environments too As a result , hostile for economicproduction . we have improved chilling tolerance in the of cultivated tomato through the technique and pollen tube elongation under low tem - vanced backcross progeny carrying selected pollen selection . peratures would effect fertilization . There - genetic characters that enable them not only Our strategyhas been to test whether selec - fore , only the selected pollen genotypes to grow and reproduce in environments tion among haploid male gametophytes ( pol - would contribute their genes to the subse - where cultivated tomatoes would experience len grains ) might have a positive , correlated quent generation . We have demonstrated , in severe chillinginjury , but also to survivetem - effect on the vegetative ( sporophytic ) genera - fact , that the haploid ( pollen ) genome can peratures just above freezing that kill culti - of genes tion resultingfrom directed selection modify the fertilization ability of individual vated types . expressed in both stages . The critical require - gametes in a manner reflecting their geno - The correlated response established be - type . Furthermore , the â?? low - temperature â?쳌 ment of this overlapping model is that speci - tween chillingtolerance in tomato pollen and fic genes that are expressed in the pollen genes amenable to pollen selection also con - the sporophyte is the first of its kind and per - grains and confer a particular physiological fer low - temperature tolerance to the resul - mits the plant breeder to select with great trait also function in the vegetative plant . tant sporophytic progeny . economy in the haploid generation . The pol - Using the pollen selection technique , we Hence , selection for these genes in the pollen len selection technique developed in this pro - phase could have a positive effect on the suc - have successfullytransferred chilling tolerance gram may prove useful in selecting for im - cess of the sporophytic phase . from a wild tomato species to the cultivated proved physiologicalefficienciesin numerous In practice , virgin stigmas are pollinated tomato . This was accomplished , without re - crops under a host of stress conditions . and exposed to a low temperature challenge . course to laborious and expensive progeny Under thesecontrolledconditions , only those testing , by applying pollen selection during RichardA . Jones , Assistant Professor , Vegetable pollen genotypes conferring germinability Crops , each subsequentbackcross . We now have ad - U.C . , Davis . Embryo callus hybrids only with great difficulty by embryo culture . and not maternal seed tissues or maternal Bruce R . Thomas The undeveloped seeds produced were care - self - pollinated embryos . David Pratt fully dissected to search for the rare embryos The embryo callus method may become a ( approximately 1 in l0 , OOO ) that had devel - valuabletool for tomato breeders . F , hybrids oped enough to then continue their develop - 8 out of 11 L . have been obtained easily for Hybridization between cultivated species ment into plants on appropriate culture peruvianum strains tested . More work will be and related wild species has been of great media . needed to determinemore precisely what pro - value for cultivar improvement . Genes that L . esculenturn and L . Hybrids between L . peruvianurn strains are suscep - portion of enhance the survival of the wild species by peruvianum can be obtained much more effi - tible to hybridization by this technique . The providing disease or insect resistance , salt tol - ciently when whole , undeveloped seeds are first backcross of some F , hybrids to L . escu - erance , cold tolerance , and the like , often placed on a culture medium suitable for the has also been achieved via embryo lenturn confer the same trait on the cultivar to which growth of callus . Under these conditions , up callus . Subsequent backcross generations are they are transferred . Fertility barriers restrict to 1 in 10 ( but sometimesonly 1 in 200 ) of the expected to arise by means of normal seeds , the number of wild species that can contri - All plants regenerated seeds form callus . so the embryo callus method appears suffi - bute genes to any particular cultivatedspecies from this callushave clearlyderived from hy - cient to completelyovercomethe fertility bar - through normal sexual crosses , but these fer - brid embryos rather than endosperm or ma - riers between the two species . tility barriers can often be overcomethrough ternal cells in the seed . All of the regenerated Although the success rate is somewhatvar - the use of special procedures . plants were diploid or tetraploid , whereas en - iable , indicating that more work will be The cultivated tomato , Lycopersicon escu - dosperm cells are triploid . Traits of the regen - needed to determine the optimum plant lenturn , hybridizes with all but two of the erated plants that resemble the male parent growth conditions to use , the embryo callus wild tomato species in the same genus by nor - ( L . peruvianurn ) , such as anthocyanin con - technique is clearly more efficient than em - Lycopersicon peruvia - mal sexual crosses . tent ( the female parent used was anthocya - bryo culture for wide crosses between wild nurn , the most distantly related species in the ninless ) , form of leaves , flowers , and fruits , and cultivated tomato species . genus , does not produce viable seeds when inability to self - pollinate , and the isozyme Bruce R . Thomas , formerly graduate student , hybridized with cultivatedtomatoes . Hybrids migration rate in gel electophoresis , proved and David Pratt , professor , ~ ~ ~ u , c . , ~ ~ ~ i ~ l ~ ~ ~ , between thesetwo species have been obtained that the plants derived from hybrid embryos Davis . CALIFORNIA AGRICULTURE.AUGUST 1982 27
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