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The pachytene bivalents of the tetraploid Cynodon dactylon var. dactylon could all be identified on the basis of characteristic morphological features including knobs, prominent chromomeres, chromosome length, long arm length, short arm length, arm ratio and relative length. The bivalents could be separated into two sets of chromosomes, D and D', with the D genome being homologous to that found in the diploids, C. dactylon vars. aridus and afghanicus. The two sets are homoeologous as shown by the occasional formation of quadrivalents and the closeness of chromosome measurements, although chromomere patterns and knobs differed. C. dactylon var. dactylon therefore appears to be a segmental allotetraploid. In prophase somatic spreads of var. dactylon two sets of chromosomes could also be separated by heterochromatic patterns. In both the diploids, vars. aridus and afghanicus, and the tetraploid the somatic chromosomes could be homologised with their corresponding pachytene bivalents. The chromosomes were of different relative lengths during the two phases. A polyhaploid obtained from a twin seedling of C. dactylon var. dactylon showed both univalents and bivalents in a diplotene spread, supporting a segmental allopolyploid origin of var. dactylon. This plant reverted back to a tetraploid state before further studies could be made. Giemsa C-banding, using barium hydroxide at room temperature for 50 minutes and 2xSSC at 60°C for 30 minutes to pretreat the slides before staining, produced telomeric bands in the position of the knobs seen in standard acetocarmine squash.

Five clones of giant type bermudagrass, Cynodon dactylon (L.) pers. vars. aridus and afghanicus Harlan et de Wet, progenies from crosses among those five, and crossed, selfed, and open pollination progeny from selected F₁ plants were evaluated for response to simazine (2-chloro-4,6-bis(ethylamino)-s-triazine). The first two generations were also evaluated for their response to ametryn (2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine). Two techniques were used. Culm cuttings, rooted in wet vermiculite, were placed into test tubes of simazine or ametryn suspensions at various concentrations or water. Culms were rated (1 to 9, 9 normal, 1 dead) for herbicide injury. Seeds were placed into petri dishes on moist filter paper, germinated in a germinator (day 35C, night 21C) and treated with 8ppm simazine or water in a greenhouse. Seedlings were rated visually for herbicide injury (7 normal, 5 affected, 1 dead) weekly, later daily, until a final drying and weighing of seedlings after all those in simazine were dead. Tolerance of all treated materials was expressed as percentage of control. There were significant differences among plants in tolerance to simazine with significance up to .001, although there was great variance within genotypes affected. The correlation between ametryn and simazine reaction was low. Tolerance scores were affected by condition of culms (significance .05), dosage, and nutrient levels. The clone by nutrient level interaction was significant at .01. Tolerance to simazine varied widely (more than 60%) among progeny of any plant as maternal parent. Progeny of reciprocal crosses between resistant and susceptible clones had similar (45 to 46) mean tolerance scores intermediate between parental scores indicating no dominance. Plants with the same cytoplasm ranged from most resistant (88%) to most susceptible (11%). Maternal effect on tolerance appears absent. The range of response for progeny of parents of any tolerance level indicates several pairs of genes are involved. Open pollination seedlings from consistently resistant plants averaged more resistant than seedlings from consistently susceptible plants. Giant bermudagrass simazine tolerance must be quantitatively inherited, possibly additive, with penetrance varying with plant condition, dosage, and other environmental constraints.