Hayes and Garber - Cucurbit Breeding
Hayes and Garber - Cucurbit Breeding Hayes and Garber - Cucurbit Breeding
248 BREEDING CROP PLANTS need not be repeated here. Yield, quality, and disease resistance are the three most important economic characters. To bring about a desirable combination of these characters, both selection and hybridization have been practiced. Selection has been used by Edgerton (1918), of the Louisiana Agricultural Experiment Station, to isolate tomatoes resistant to wilt (Fusarium lycopersici) . The improved technic followed is worthy of consideration. Seeds of a particular variety were planted in soil which had been sterilized previously and then inoculated with a pure culture of the wilt-producing organisms. When seedlings showed wilt infection they were pulled and discarded. Only plants which showed resistance were transplanted to the field. Tomatoes had grown continuously for eight or ten years on this field and it was known to be heavily infected with the wilt fungus. The use of this method permits a smaller acreage and insures the contact of each plant with the wilt organism. A selection made from a row of Acme grown in 1909 named " Louisiana Wilt-Resistant" was extremely wilt resistant but possessed other characters which made it undesirable for Louisiana conditions. Selections from the progeny of crosses between this form and Earliana showed considerable promise. Durst (1918) reported the result of five years' selection for resistance to Fusarium of tomatoes. Varieties were found to differ a great deal in their resistance and unfortunately the most resistant ones produced poor fruit. After five years, some of the better strains stood up in soil which proved fatal to the original varieties. In addition to disease resistance, the selections also showed good yielding ability. Of seventy-four lots grown one year the highest fourteen yields were produced by selected strains. Whether selection alone or hybridization and selection together are to be used as a means of improving a crop is dependent upon the nature of the material. If the character combination is not already present, the only practical means of bringing it about is crossing followed by selection. Cross-Fertilized Vegetables Crops have previously been classified as belonging to four groups according to their mode of reproduction. Cross-fertilized vegetables may be roughly divided into three main divisions;
BREEDING OF VEGETABLES 249 1. Those which are normally cross-pollinated but which set seed freely on selfing and show no evidence of sterility. 2. Those which are wholly or partially self-sterile. 3. Those which are cross-fertilized owing to the dioecious condition. Much more study of the mode of pollination of vegetables is necessary before it is possible accurately to classify vegetables according to their mode of reproduction. The crops here considered have been purposely chosen as illustrations of breeding results within these three groups. RADISH Origin, Inheritance, and Breeding. The cultivated radish, Raphanus sativus, was grown by the ancient Greeks and Romans. There has been considerable discussion as to its origin. Some writers have thought that the cultivated form with its fleshy root arose directly from R. raphanistrum. This belief was apparently substantiated by experiments in which the wild form was grown under cultivation and after several years cultivated radishes were obtained. Riolle (1914) tested this hypothesis by a controlled experiment. The wild form was grown under cultivation and self-fertilized. Three years of selection failed to produce roots which resembled the fleshy roots of R. sativus. On the other hand, when the wild and cultivated forms were both grown on the same plot and seed was saved from the wild form, it was found to be an easy matter, after three years' selection, to obtain roots which resembled the fleshy roots of R. sativus. These results were believed to be due to natural crossing of the wild and cultivated forms. This hypothesis was tested by making an artificial cross. Segregation for root condition occurred in F 2 . This led Riolle to conclude that former experiments in which cultivated radishes were obtained from the wild through selection were best explained through natural crossing. R. sativus roots contain sugar while wild roots contain no sugar, FI crosses contain less sugar than the cultivated forms. The presence of starch in the root of the wild radish, particularly in the bark, is a character which separates it from the cultivated varieties. This proved a dominant in crosses. Cultivated radishes show various color intensities. Color is apparently inherited in much the same manner as in other crops. Individual
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248 BREEDING CROP PLANTS<br />
need not be repeated here. Yield, quality, <strong>and</strong> disease resistance<br />
are the three most important economic characters. To bring<br />
about a desirable combination of these characters, both selection<br />
<strong>and</strong> hybridization have been practiced.<br />
Selection has been used by Edgerton (1918), of the Louisiana<br />
Agricultural Experiment Station, to isolate tomatoes resistant<br />
to wilt (Fusarium lycopersici) . The improved technic followed<br />
is worthy of consideration. Seeds of a particular variety were<br />
planted in soil which had been sterilized previously <strong>and</strong> then<br />
inoculated with a pure culture of the wilt-producing organisms.<br />
When seedlings showed wilt infection they were pulled <strong>and</strong> discarded.<br />
Only plants which showed resistance were transplanted<br />
to the field. Tomatoes had grown continuously for eight or ten<br />
years on this field <strong>and</strong> it was known to be heavily infected with<br />
the wilt fungus. The use of this method permits a smaller<br />
acreage <strong>and</strong> insures the contact of each plant with the wilt<br />
organism. A selection made from a row of Acme grown in 1909<br />
named " Louisiana Wilt-Resistant" was extremely wilt resistant<br />
but possessed other characters which made it undesirable for<br />
Louisiana conditions. Selections from the progeny of crosses<br />
between this form <strong>and</strong> Earliana showed considerable promise.<br />
Durst (1918) reported the result of five years' selection for<br />
resistance to Fusarium of tomatoes. Varieties were found to<br />
differ a great deal in their resistance <strong>and</strong> unfortunately the most<br />
resistant ones produced poor fruit.<br />
After five years, some of the<br />
better strains stood up in soil which proved fatal to the original<br />
varieties. In addition to disease resistance, the selections also<br />
showed good yielding ability. Of seventy-four lots grown one<br />
year the highest fourteen yields were produced by selected<br />
strains.<br />
Whether selection alone or hybridization <strong>and</strong> selection together<br />
are to be used as a means of improving a crop is dependent upon<br />
the nature of the material. If the character combination is not<br />
already present, the only practical means of bringing it about<br />
is crossing followed by selection.<br />
Cross-Fertilized<br />
Vegetables<br />
Crops have previously been classified as belonging to four<br />
groups according to their mode of reproduction. Cross-fertilized<br />
vegetables may be roughly divided into three main divisions;
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