Various techniques have been employed to identify and select genotypes with superior stalk quality. Zuber and Grogan (Crop Sci. 1:378) measured stalk strength mechanically, where they determined the pressure (in load lbs.) to crush a mature stalk section. They also determined weight of a stalk section and rind thickness. Studies of these traits by Loesch, Zuber, and Grogan (Crop Sci. 3:173) indicated they were quantitatively inherited. Recurrent selection for stalk crushing strength through five cycles has increased it by 57 load-kg per cycle.
We used reciprocal translocations for locating genes affecting crushing strength, stalk section weight, and rind thickness. Twenty translocation stocks in M14 background were obtained from W. A. Russell. M14 has low crushing strength, low stalk section weight and thin rind. Each translocation stock was crossed to B37 and B14A; both of these lines have excellent stalk quality. Each semisterile F1 was test-crossed to Oh43 and N31, each with low crushing strength, low stalk section weight, and thin rind. Mean values for the five inbred lines are given in Table 1.
Tables 1 and 2.
The testcrosses were grown in 1975 at Columbia, Missouri, and Belleville, Illinois. Plants were classified as fertile or semi-sterile by anther examinations and verified by seed-set at harvest. Stalk sections from the second internode above ground level were evaluated. Data were analyzed separately for each testcross as illustrated in Table 2 for stalk section weight involving (T1-9c x B14A) Oh43. Mean differences between fertile and semi-sterile plants (classes) for these characters are given in Tables 3, 4, 5, and 6. Significance implies that a gene or genes might be located in either or both arms involved in that specific translocation. When two translocations involving a common arm show a significant difference between the fertile and semi-sterile plants, it indicates that a gene for the trait under study is present on that arm. However, designation of a gene(s) in a specific chromosome arm does not rule out the possibility that the gene might actually be in the other arm of that chromosome but close enough to the break point to show linkage. Arms that could not be completely ruled out have been noted as 'possible'. A summary of the chromosome arms is given in Table 7 for stalk section weight, in Table 8 for crushing strength, and in Table 9 for rind thickness.
Additional translocations involving the following arms need to be studied further: 1L, 3L, 5S, 6S, 6L, 8S, 10S, and 10L. The testcrosses marked - have been produced and will be reported later. This study indicates that the three stalk characters are conditioned by several genes. Chromosomes or chromosome segments favorable to stalk quality may be transferred into breeding populations through translocations as described by Burnham (In: Plant Breeding, A Symposium, ed. K. J. Frey:139-187). It may also be possible to transfer desirable genes through use of B-A translocations.
Manjit S. Kang, M. S. Zuber, Oval Myers, Jr.,* and T. R. Colbert**
*Southern Illinois University
**Present address: Funk Seeds International, Bloomington, Illinois
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