One hundred and ninety grain sorghum hybrids, produced by crossing 10 male‐sterile lines with 19 fertility restorers, were compared with their parents over 2 years at Lincoln, Nebraska. The hybrids average 20% higher in grain yield, 0.5 lb. heaver in weight per bushel, 4.5 inches taller, and 2.5 days earlier than the mean of the parents. The yield advantage of the hybrids resulted mainly from increases in nmnber of seeds per head and, to a lesser extent, from increases in seed weight. Heterosis for yield was not expressed as increased tillering.The slight increase in weight per bushel resulted front slightly greater heterosis for seed weight than for seed volume.The hybrids were taller than their parents because they had longer stems, peduncles, and heads. Heterosis for stem length was manifested in the length rather than the number of internodes. It seems that the factors controlling the number and length of internodes differ from those determining peduncle and head lengths.The grain produced by the hybrids averaged lower in protein content than that produced by the parents. However, because of their higher yield, the hybrids averaged 16% higher than the parent in crude protein per acre.
T HIS paper reports the breeding behavior of a nondehiscent anther character which first appeared in a cross involving an African sorghum variety. Anatomical and histological differences between normal and nondehiscent anthers are also presented. MATERIALS AND METHODS
Male sterility, controlled at one locus, was discovered in 1963 at Sainaru after seed of a Nigerian sorghum had been irradiated with Co60. Crosses were made and the expression of the sterility remained stable in different genetic backgrounds and in a range of climatic conditions. Crosses with other reported genetic steriles indicate that the sterility found is governed by a new factor. The symbol ms7 is proposed.The male sterility has been used to assist the breeding program by the development of a sorghum composite.
A large‐seeded variety of sorghum, ‘Big Seed’, and a small‐seeded variety, ‘Norghum’, their F1 and F2 cross generations, and the two first backcrosses were investigated to gain a better understanding of how seed size is inherited and to assess the possibility of increasing seed size through selection. A preliminary study indicated that a 300‐seed sample from each plant would give adequate precision.Population means and variances provided the basic data from which conclusions were drawn. All populations were approximately normally distributed on the original scale. Transformation to √Y‐2 caused the largeseeded parent to depart from normality but eliminated the correlation between means and variances. Gene action appeared to be almost entirely additive. Evidence for dominance or epistasis as an important contributor to seed size was lacking. A minimum of 3 or 4 genetic factors or blocks of genes, primarily additive in their effect, appear to control seed size.Heritability for seed size was estimated to be 60% indicating that considerable progress could be made in shifting mean seed size by selecting and recombining large‐seeded F2 plants.
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