K. L. Mehra’s research while affiliated with Oklahoma State University and other places

Cytogenetical studies were conducted in 8 backcrosses and 76 F2 plants of the interspecific hybrid Setcreasea brevifolia × S. purpurea.Wide range of morphological variation and different types of recombinations between the parental characters were recovered in the F2 progeny.Meiosis was observed to be irregular in the parents, F1, backcrosses and F2 plants analyzed. The irregularities observed were the presence of multivalents and univalents besides bivalents at metaphase I, lagging chromosomes and chromosome bridges with fragments at anaphase I & II and micronuclei at the dyad and tetrad spore stages. The frequency of trivalents was low in the backcrosses. Based on the chromosome associations at metaphase I, the probable genomic formulae were assigned to the materials studied.Relationships between S. brevifolia and S. purpurea were discussed in the present investigation. These species seem to be closely related with each other.

Cytogenetical studies were undertaken in ten interspecific hybrids of Setcreasea brevifolia × S. pallida.Taxonomical descriptions of the parents and ten interspecific hybrids were presented. Chromosome behavior during the process of meiosis was analysed in all of the hybrids. Chromosome association of six univalents and six bivalents was observed at metaphase 1 in 2 to 28% of the cells in the different hybrids. In one of the ten hybrids, as many as five trivalents were observed in two per cent of the cells at metaphase I. Successive stages of meiosis were observed to be irregular. These irregularities were the presence of irregular disjunction, lagging chromosomes, dicentric chromosome bridges and fragments at anaphase I; lagging chromosomes at anaphase II and several micronuclei at both the dyad and tetrad spore stages.Cytological analysis of the ten interspecific hybrids of S. brevifolia x S. pallida seemed to suggest that one of the two putative diploid parents of the tetraploid S. brevifolia is S. pallida. With the aid of the method of extrapolated correlates the taxonomical description of the other putative diploid parent of the tetraploid S. brevifolia was presented.Relationship of S. brevifolia with S. pallida was discussed in the light of the present investigation.

Cytogenetical studies were undertaken in Setcreasea brevifolia, S. purpurea and in their eight interspecific hybrids.

Cytogenetical studies were undertaken in two interspecific hybrids of Setcreasea purpurea × S. pallida.Taxonomical descriptions of these two hybrids were presented. Chromosome behavior during the process of meiosis was studied in these hybrids. Chromosome associations of six bivalents and six univalents were observed in 50% and 66% of the cells in the hybrid-1 and −2 respectively. Successive stages of meiosis showed several irregularities. These irregularities were the presence of lagging chromosomes, chromosome bridges plus fragments, and unequal distribution of chromosomes at anaphase I; lagging chromosomes at anaphase II; and micronuclei at both the dyad and tetrad spore stages. Chromosome number was observed to be variable (range being 5 to 10) in the pollen grains.Relationship between S. purpurea and S. pallida was discussed in the light of the present investigation.RIASSUNTOSono stati intrapresi degli studi citogenetici su due ibridi interspecifici di Setcreasea purpurea × S. pallida.Vengono qui presentate le descrizioni tassonomiche di questi due ibridi. Sono state osservate associazioni cromosomiche di sei bivalenti e sei univalenti nel 50% e nel 66% delle cellule, rispettivamente dell'ibrido-1 e dell'ibrido-2. Gli stadi meiotici successivi presentavano varie irregolarità, consistenti nelle presenza di cromosomi isolati, ponti cromosomici con frammenti e distribuzione ineguale dei cromosomi all'anafase I. Sono stati inoltre riscontrati cromosomi isolati all'anafase II e micronuclei, sia allo stadio di diade sia a quello di tetrade. Si è osservato che il numero cromosomico nei granuli pollinici era variabile da 5 a 10.La relazione tra Setcreasea purpurea e S. pallida viene discussa alla luce della presente ricerca.

In one of the hybrids involving the Tropical and Mediterranean types of the Dichanthium annulatum complex, an unreduced egg of the Tropical type appears to have been fertilized by a reduced gamete of the Mediterranean type. This hybrid looked very much like Dichanthium papillosum Stapf with respect to several cytological and morphological characters, and its F2 progeny showed considerable variation in the direction of D. papillosum Stapf, D. annulatum (Tropical type) and D. annulatum (Mediterranean type) with respect to several morphological characters. Also, different types of recombinants between these three taxa were recovered in the F2 progeny.