Hayes and Garber - Cucurbit Breeding
Hayes and Garber - Cucurbit Breeding Hayes and Garber - Cucurbit Breeding
204 BREEDING CROP PLANTS general rule can be given and the only sure means of determining the value of a cross is by the experimental test. Results have shown that FI crosses between good yielding varieties which differ from each other in several characters frequently yield considerably more than either parent and more than pay for the trouble of producing crossed seed. Thus the tests made in Con- FIG. 47. Fi cross of Minn, self-fertilized strains No. 1 X No. 4. necticut (Jones et al, 1919) and those carried out in Minnesota (Hayes and Olson, 1919) showed that/^i crosses between selected eight-rowed flints and dents very frequently exceeded either parent in yielding ability. For each growth character in which the parent varieties differ there is usually an intermediate condition in FI. There is a tendency for a partial dominance and the first generation often exceeds the average of the parents in most
MAIZE BREEDING 205 of its characters. Fi crosses are of value from the standpoint of earliness. Thus a cross, studied at Minnesota in 1919, between Squaw flint and Minnesota No. 13, approached the dent parent in height of plant and the flint parent in earliness and exceeded both in yield. Such a cross would be of much value as a silage or husking variety under northern conditions. The production of crossed seed is not very difficult. The varieties to be crossed may be planted in alternate rows and the tassels removed from one variety before any of the pollen has matured. Seed produced by the detasseled variety is known as first generation crossed seed. If the varieties to be crossed differ in maturity they should be planted at different times so that both bloom at about the same date. Isolation of Homozygous Strains. Shull (1908, 1909) first suggested the utilization of crosses between self-fertilized strains as a means of increasing yield in corn. Such crosses often give very high yields. The chief objections to this method are that self-fertilized strains are usually of very low yielding capabilities and that the seeds from selfed lines are usually much smaller than from normally pollinated corn. Even though crosses between self-fertilized lines yielded very vigorously, the method has not seemed commercially desirable. Low yields of seed per acre would increase the cost of seed. Under unfavorable conditions the food supply of the seed might not give the young FI plant a vigorous start. Jones (1918) has made a suggestion which removes some of these objections. After isolating selfed strains, tests are made to determine which four biotypes are most desirable as parents. Suppose these are numbered 1, 2, 3, and 4 respectively. Numbers 1 and 2 are crossed, also 3 and 4, by detasseling all of one biotype in each group. Seed from the plant^ of each detasseled biotype is then planted in alternate rows in an isolated plot and all of one combination, as 3 X 4, detasseled. Seed from these detasseled rows is used for commercial planting. This method seems worthy of more extensive trial. Such a cross was compared at the Connecticut station with the best dent variety obtained from a varietal survey followed by a variety test. The highest yielding dent variety gave a yield of 92 bu. while the cross under similar conditions yielded 112 bu. Every investigator who has produced self-fertilized strains of corn has been impressed by the large number of undesirable
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204 BREEDING CROP PLANTS<br />
general rule can be given <strong>and</strong> the only sure means of determining<br />
the value of a cross is by the experimental test. Results have<br />
shown that FI crosses between good yielding varieties which<br />
differ from each other in several characters frequently yield considerably<br />
more than either parent <strong>and</strong> more than pay for the<br />
trouble of producing crossed seed. Thus the tests made in Con-<br />
FIG. 47. Fi cross of Minn, self-fertilized strains No. 1 X No. 4.<br />
necticut (Jones et al, 1919) <strong>and</strong> those carried out in Minnesota<br />
(<strong>Hayes</strong> <strong>and</strong> Olson, 1919) showed that/^i crosses between selected<br />
eight-rowed flints <strong>and</strong> dents very frequently exceeded either<br />
parent in yielding ability. For each growth character in which<br />
the parent varieties differ there is usually an intermediate condition<br />
in FI. There is a tendency for a partial dominance <strong>and</strong> the<br />
first generation often exceeds the average of the parents in most
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