MECHANISMS AND INHERITANCE OF FIRST DIVISION RESTITUTION IN HYBRIDS OF WHEAT, RYE, AND AEGILOPS-SQUARROSA

First division restitution (FDR) in intergeneric Triticeae hybrids pro vides an important meiotic mechanism for the production of amphidiploi ds without the use of colchicine and similar chemicals. The genetic co ntrols of FDR were investigated by examining microsporogenesis and fer tility in F-1 hybrids of two- and three-way crosses of durum wheat (Tr iticum turgidum L val. durum) cultivars Langdon (LDN) and Golden Ball (GB),'Gazelle' rye (Secale cereale L.), and one accession (RL5286) of Aegilops squarrosa L. The results from two-way crosses indicated that the first meiotic division varied, depending on the hybrid. GB crossed with Ae. squarrosa developed tripolar spindles and prevented congrega tion of chromosomes at the equatorial plate. The hybrid of GB with rye had a delayed first division. But, the hybrids of LDN with both Ae. s quarrosa and rye had a high frequency of FDR. Analysis from the three- way crosses indicated that inheritance in rye crosses differed from th ose with Ae. squarrosa. FDR segregated in a 1:1 ratio in the rye cross , suggesting that the FDR is controlled by a single gene from LDN. How ever, FDR fit a 1:3 ratio in the three-way crosses with Ae. squarrosa. Cytological data suggested thar tripolar spindles are a major factor preventing FDR in Ae. squarrosa crosses. Some progenies from the three -way cross with rye had a high frequency of monads that resulted from second division failure of FDR cells.