Cytological Analyses in ‘Niagara Branca’ Grape and in Its Somatic Mutant ‘Niagara Rosada’

An investigation in the microsporogenesis of two cultivars of grapes (Vitis L.), were carried out on 'Niagara Branca' and on its somatic mutant 'Niagara Rosada', aiming at ascertaining the normality of the microsporogenesis. Some possible changes have been checked on chromosome number in somatic cells, pollen size and fertility, stomatal size and frequency, which related to the somatic mutant 'Niagara Rosada', thus increasing the information already obtained regarding 'Niagara' grapevines. The microsporogenesis occurred normally in both cultivars and cytomixis observed only among pachytene cells. A low percentage of precocious chromosome segregation was noticed in metaphase I and II, as well as a very low percentage of laggard and stickiness chromosomes in anaphase I and II. Less than 1% of tetrads showed microspore alterations. The mean values of the meiotic index and pollen grain fertility were high. However, no association were observed between the occurrences of chromosome abnormalities and the variation in the anther number (five to seven) seen among flower buds. The cultivars showed the same chromosome number, n=19 at diakinesis and 2n=38 in somatic cells, and did not differ in regards to stomatal size and frequency. It seems that the difference between the cultivars lied at gene level. Due to the very low percentage of abnormalities and to high pollen grain fertility, the plants analyzed could be very well employed in breeding programs for the grapevines.