A new type of non-chromosomal stripe from Taiwanese maize
--Bor-yaw Lin and Hao-Jan Yu
A variant plant was found in the fall planting of 1992, among more than one thousand individuals of a local maize race called Tainan White, the origin of which is sketchy. This race has been cultivated on the island for more than eighty years, presumably originating from the United States through Japan many years ago. Based on Chang's literature review (Know-You News Letter 157:76-83, 1993), the earliest local cultivated maizes included White Flint, Hickory King, Large Yellow, Longfellow and Chiachow. Among these, the phenotype of Hickory King is closest to that of Tainan White, including dent kernels, large grain, white endosperm, ears with 8-10 kernel rows, tall stand, and relatively slow maturity rate (60-75 days). Total SDS-protein gel electrophoretic analysis revealed that the protein pattern of Tainan White was similar to that of Hickory King, a subrace of Southern Dent.
This variant plant exhibited white stripes on all leaves, and the stripes extended from leaf blades to sheath and to the internode below the sheath. Most striped areas were white or yellow white, but some were light yellow green. The transition from green to white tissues was sharp and clear in some areas but was filled with yellow greenish tissues in others. The width of stripes varied, from about 2 cm to less than 0.5 cm, but there was no striation on this plant or its progeny. In those leaves with two halves divided by the midrib, no displacement of the midrib from the leaf center was evident. This plant was somewhat shorter than the surrounding plants, but since Tainan White is not a uniform line, the difference in height may not be part of the variant phenotype.
This plant was self-pollinated to result in an infected ear with about 200 clean healthy kernels. Twenty kernels were planted the following spring and all of them were destroyed by insects. Ten more kernels were immediately germinated in late spring and transplanted to pots, which were placed on the roof of a head house (the only place that we could find by then) with proper protection from insects. The plants did not grow normally, because of inappropriate pot size, constant high temperature (av. 40 to 43 C) and periodical water shortage. Yet, one plant managed to have enough pollen for crossing to produce 85 kernels.
Preliminary crosses involving this variant demonstrated that it was inherited in a manner indicating that the gene responsible for the striped phenotype is not located on chromosomes. First, the variant, after it was crossed reciprocally with hybrid W22/W23 plants, gave different results. The variant, when mated as female, produced an ear with a normal phenotype like that of sib ears, without any small or other off-type kernels. Eighty-five kernels were germinated before planting in the field and resulted in 73 seedlings; 70 of these had yellow greenish leaves which turned yellow white at the 6-leaf stage and died. Three others had striped leaves; two were about two-thirds as tall as their sib plants, and stalks were thinner and leaves were narrower than their sib counterparts. Their leaves had yellow greenish stripes which turned white at maturity and produced normal pollen. The striped leaves had about 50% white area. The last plant resembled its female parent with about 25% white area and had a normal size and height. The reverse cross gave an ear of normal appearance, 80 kernels from the ear were planted directly to the field to give rise to 60 plants, and all were green and tall, indistinguishable from hybrid plants of the same background planted in the same field. Second, a small-scale ear mapping analysis using a limited number of kernels (from a segment of the ear with 10, 10-kernel rows) revealed clonal distribution of variant kernels. Four variants were observed, three of these appeared in the same row, with one and two green sib plants between them, and the last variant was found in the adjacent row at the same relative position at the three others.
In an attempt to understand if the chloroplast was affected in the variant tissue, fresh mature leaves were sectioned with a razor blade and examined under light and phase microscope. Two different leaves were analyzed: one was from one of the three viable striped plants germinated from kernels borne on the variant pistillate plant crossed with the W22/W23 hybrid pollen, and the other was from a normal green plant derived from the reciprocal cross mentioned above. For the striped leaf, most cells had no visible chloroplasts, but a few others had less than three yellow greenish chloroplasts. There were 9 to 13 green chloroplasts per cell in green and yellow greenish tissues of the same leaf. The color of these chloroplasts was not uniform; there was a gradient of color intensity. More light-colored chloroplasts were present in the yellow greenish tissue than the green one. The normal leaf from the reciprocal cross had about 23 chloroplasts, with color intensity similar to the green tissue of the first leaf.
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