Twenty‐nine recently introduced diploid (2n = 2x = 20) accessions of section Arachis plus an A. correntina (Burk) Krap. et Greg. nom. nud. control were hybridized to the diploid A‐genome species A. duranensis Krap. et Greg. nom. nud. (ace. 7988), the diploid B‐genome species A. batizocoi Krap. et Greg. (acc. 9484), and with two subspecies of the A‐B genome (2n = 4x = 40) A. hypogaea cultivars NC 4 and Argentine. Most attempted crosses were successful and the resulting plants were vigorous. However, A. batizocoi × accession 30008 hybrids died as seedlings and A. batizocoi × accession 30017 produced only dwarf plants. The 710 diploid F1s from A. batizocoi were generally sterile, while those from A. duranensis had fertility ranges from 5% to 84%. Meiotic chromosome relationships in diploid crosses were cytologically evaluated in 185 plants plus tester accessions. Most taxa in section Arachis have an A genome, only A. batizocoi accessions have a B genome, a D genome is represented by accessions 30091 and 30099, and two other genomic groups, represented by accessions 30011 and 30033, may be present in the section. Most cytological differentiation was found among species originally collected in southern and eastern Bolivia. On the other hand, species collected at the extremes of the distribution of section Arachis species (northern Argentina to north‐central Brazil) were cytologically very similar. Evidence is presented for speciation in Arachis being associated with both genetic differentiation and with translocated chromosomes. All taxa in the section except the D‐genome species are believed to be cross‐compatible with A. hypogaea, so germplasm introgression from most Arachis species should be possible.

Eighteen accessions of a diploid wild peanut species (Arachis duranensis) were analyzed using morphological, intercrossing, cytological, and RFLP data. Abundant variation was found for morphological characters and for RFLP patterns both between and within accessions, and each accession could be uniquely identified by RFLP pattern. Several plants were found to be F1 hybrids between different accessions, indicating that intercrossing had occurred when these were planted for seed increase. Patterns of RFLP diversity were found to correspond with geographic distribution. Analysis of the number of RFLP fragments observed per accession indicates that additional field collections of this complex of taxa will yield additional genetic variability.

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Desynapsis is defined as a condition in which chromosomes pair initially but as the meiotic division progresses, the chromosomes start falling apart. At diakinesis one can see all or most of these lying as unpaired chromosomes. The occurrence of unpaired chromosomes (univalents) is due to the failure of chiasma formation and is considered to be under the control of recessive genes when present in homozygous condition (Riley and Law 1965). Spontaneous or directed mutation of a single gene leads to unpairing of chromosomes which ultimately result in more univalents and proportionally less bivalents. This gene is sensitive to temperature variation and X-rays (Ahloowalia 1969a, Riley and Miller 1966, Sjodin 1970) and thus desynapsis is also the result of interaction between genotype and environment. Thus the stability of this gene has not been established yet. This paper deals with some of the cytogenetic observations recorded on desynaptic plants in pearl millet. Material and methodsDuring the cytological investigations of chromosomal abnormalities in the genetic stocks of pearl millet, BG-32 (Bold grain) was showing a high frequency of univalent chromosomes. Many plants in this genetic stock showed the desynaptic condition of varying degrees. The young panicles of these plants were collected and fixed in alcohol: acetic acid (3:1) for 24 hours, and then smears were made in acetocarmine. The observations were made from the fresh slides and photographs were taken. Pollen fertility on the basis of stainability reaction with potassium iodide (KI) was determined. Seeds per square cm were calculated under selfed and crossed conditions. ResultsIn normal as well as in the desynaptic plants the chromosome number was 2n=14. Normal plants showed 7II (Fig. 1). In desynaptic plants the bivalent variation was from 0-5 bivalents per cell (Table 1 and Fig. 2). The average number of bivalents were 1.934 per pollen mother cell. The univalents present were scattered around without any set pattern. Metaphase I was very irregular. The spindle apparatus was formed but all the chromosomes did not lie along the equatorial plate.