- Two diverse genotypes of tall fescue, Festuca arundinacea Schreb (6X=42), with normal fertility, produced upon intercrossing, vigorous F
hybrid plants that were sterile. One parent genotype (P₁)
was from P. I. 234-906, introduced from Switzerland and the other
(P₉) was an introduction from Turkey, P. I. 174-209. P₁
differ in anthesis date by 30 days.
Both parents and F ₁
genotypes were observed to have normal
meiotic behavior, but the F
plants did not shed pollen because of
failure in microspore mitosis.
The meiotic process was similar in the parental and hybrid
genotypes. The average number of bivalents per microsporocyte
was 20.70, 20,44 and 20.13 for P₁, P₉ and the hybrid respectively.
Limited abnormal chromosome behavior was observed in both parental
and hybrid genotypes. They were expressed as univalents, pseudobivalents,
occasional multivalents and fragments at diakinesis. Chromosome
stickiness was observed at metaphase-I in all genotypes.
The frequency of univalents per microsporocyte was 0.16, 0.27 and
0.59; while the frequency of multivalents was 0.04, 0. 08 and 0.10
for P₁, P₉ and the hybrid respectively.
Laggards at anaphase I and II, and micronuclei at the telophase
I and quartet stage were observed. Spontaneous chromosome breakage
occurring in early prophase was believed to have resulted in the
observed fragments at diakinesis. The diakinesis fragments and
univalents were the probable origin of the anaphase laggards and
subsequent micronuclei in the quartets.
Pollen fertility in the parental genotypes was measured using
pollen germination in vitro followed by staining with propioniccarmine.
There was no significant difference between the average
of percent of pollen classified as sound by this method, and the average
percentage of quartet groups with no micronuclei, which is an
indicator of pollen normality.
The hybrid genotypes exhibited normal anthesis, with well
formed anthers, however they failed to dehisce and produce normal
pollen. Free normal microsporocytes were produced following the
quartet stage in the hybrid, but they remained uninucleated and thus
degenerated to shriveled pollen. The pistil in the hybrid appeared
normal and limited evidence suggests they are fertile.
Abnormalities in chromosome behavior which lead to the loss
of genetic material as micronuclei in the microsporocyte, can explain
the percentage of abnormal pollen observed in the parental genotypes, but not in the hybrid. Only 30% pollen sterility was expected in the
hybrid, however complete sterility was observed. Seventy percent
of the quartet groups were normal but failed to develop into normal
pollen. Factors, other than chromosome abnormalities, acting in
the microsporogenesis process are believed to be causing the sterility
found in the hybrid. A possible male-sterile hybrid due to geneticcytoplasmic
interaction which is expressed at the mitotic division
of the microspores is postulated.