| LAMPRECHT (1945) reported similar results in interspecific hybrids of
Phaseolous species. He obtained sterile plants when Hyp (hypogeal
cotyledons) and Ext (exterior stigma) genes of P. multifluorous
were transferred to the nuclear genome of P. vulgaris in P. vulgaris
cytoplasm. All other genes examined were reciprocally transferred from one
species to the other by backcross and selection procedures. He suggested
that Hyp and Ext genes were plasma-specific, and produced
male sterile P. vulgaris plants in P. vulgaris cytoplasm,
Also, Hyp and Ext were unstable in P. vulgaris cytoplasm
and frequently mutated to Epi and Int alleles, respectively.
These alleles normally occur in P. vulgaris. Similarly, KIHARA (1951)
reported that the gene controlling black glume color was preferentially
transmitted and frequently mutated to an allele for yellow glume in T.
aestivum cytoplasm (and produced mosaics) when transferred from an Ae.
caudata chromosome to a T. aestivum chromosome. In these instances
species-specific nuclear genes could not be transferred from one diploid
species to another, because of incompatable nucleo-cytoplasmic interactions.
However, species-specific nuclear genes of the diploid species can be transferred
to the nuclear genome of the related polyploid species. The resulting alloplasmic
plants with critical nuclear genes from different diploid species can be
crossed with one another or with critical diploids to determine the specificity
of the nucleo-cytoplasmic interactions. For example, MAAN and LUCKEN (1972)
reported that wheat R-lines derived from crosses involving T. boeoticum-Ae.
squarrosa amphidiploid did not restore fertility to alloplasmic T.
aestivum with Ae. speltoides or T. araraticum cytoplasms,
where as wheat R-lines derived from crosses involving Ae. speltoides
or T. araraticum did restore fertility to wheat with cytoplasms of
these species. These results indicated that Ae. speltoides and T.
boeoticum have different cytoplasms and Ae. speltoides and T.
araraticum have similar cytoplasms. Therefore, T. aestivum lines
with cytoplasm and critical nuclear genes from diploids can be used to study
nucleo-cytoplasmic interactions in the genetic background of hexaploid T.
aestivum. Also, alloplasmic wheats having cytoplasm of diploid species
and with or without the critical nuclear genes may be crossed with other
related diploids (which are cross-incompatable at the diploid level) and
their interactions may be examined in F1hybrids . |