Mulberry exehibits a high degree of polyploidy ranging from haploidy to docosaploidy and its various species are being cultivated for foliage to practice sericulture and edible fruits. Triploid mulberries for sericulture porpuse and higher polyploids are proved to be superior.  The cultivar Suvarna-2 is an improved high leaf yielding triploid in south India. The meiotic behavior of this cultivar has been presented here. Meiosis was highly irregular. Various anomalies such as univalent, bivalents, trivalent, hexavalent, loose association, unequal separation and precocious movement of chromosomes and laggards have been observed in pollen mother cells. These irregularities prevented the formation of viable gamete that leads to pollen sterility.

In mulberry (Morus spp.), the process of selection of promising hybrids from F1 population requires the screening of a large number of progenies and a long period. To develop a simple and faster approach for screening, studies were conducted using F1 seeds of two crosses. The details of screening studies conducted in relation to seedsize and seedling-size are reported separately in two parts. In this part, the F1 seeds were size-graded as small, medium and large seeds; their progenies were raised separately and screened in nursery. There was a considerable degree of variation in size of seeds and medium-size class seeds were in high percentage in both the crosses. The length, width and weight of seeds were also varied between the seed size classes significantly in both the crosses. The seed size classes differ with high significance in shoot length and Root collar diameter and also differ significantly in root length and weight of seedlings. The positive correlation between the seed size and growth of seedlings, seed size and germination, seed size and seedling survival in nursery indicated that size-grading of seeds and rejection of small seeds in the beginning of screening process itself, may help to increase the efficiency of screening by increasing the chances of getting superior hybrids from limited progenies. However, confirmation on the performance of large seedlings from small seed size class may help to draw conclusion. Hence, the studies are continued with size-grading of seedlings in the next part of screening study.

Abstract:In continuation of studies on the effect of seed size on growth, made under part-I, the effect of seed size and seedling size are studied jointly by size-grading of seedlings into three classes under each seed-size class, with 2700 F1 promising genotypes of two crosses. The combined population was screened in two steps, adopting comparison tree method. In step-1, transplanted seedlings (transplants) with closer spacing were screened based on shoot weight for a period of two crops and 487 genotypes were shortlisted based on higher superiority percent. In step-2, these 487 transplants were replanted with wider spacing and screened using three parameters for a period of four crops. In each crop, the genotypes which showed superiority percent value more than Minimum Selection Standard for the parameters studied, were shortlisted. Among 22 genotypes shortlisted finally, 18 have come from large seed-size class and the remaining four are also from long seedling-size class of medium seed-size class. This clearly established the importance of size-grading of seeds and seedlings in screening process. As the chance of getting any promising genotype from small seeds is remote, they could be rejected before sowing and as it is also true with small seedlings they could be rejected at nursery stage screening. The tracking of juvenile performance of shortlisted genotypes indicated that, shoot length and root collar diameter are more reliable parameters for assessing the growth of seedlings at nursery. Comparison tree method is found to be highly useful for shortlisting of transplants in mulberry.