Pollen dispersal in wheat (T. aestivum L.)

S.C. ANAND and S.C. SHARMA

Punjab Agricultural University, Ludhiana, India

With the discovery of cytoplasmic male sterility and fertility resotration mechanism in wheat (WILSON & Ross, 1962; SCHMIDT, JOHNSON & MANN, 1962) great deal of interest was created for the exploitation of hybrid vigour by the production of 'hybrid wheat'. Wheat being a self-pollinated crop, the problems associated with the production of hybrid seed on commercial scale was due to poor pollen shedding and dispersal (WILSON, 1968). MENGE et al., (1965), ANAND and BERI (1971) showed that cross pollination of wheat was affected by pollen load and wind direction. ZEFEN (1968) reported that the number of pollen grains above a wheat field was an important factor affecting seed set. To measure pollen load, Bitzer and Patterson (1967) exposed vaseline coated slides in the field and the pollen grains trapped on the slides were counted. The present study was undertaken to measure pollen availability in wheat at various distances and in all the four directions of the pollen source under field condition.

Materials and Methods

Wheat variety C273 was used to study pollen dispersal C273 is a tall cormeroial cultiver and it was planted in a three square meter plot. During period of anthesis, microscopic slides fitted with adhesive tape were fixed to trap the pollen grains. They were placed towards east, west, north and south at 22, 44, 66 and 83 cm from the first row of the pollen source. Three slides were fitted just below spike level and three just below spike level and three were placed at the ground level at each distance and direction. The slides were mounted in the morning and removed in the evening for three successive days. The exposed area of the adhesive tape was 2.5 x 2.0 cm (5 cm²). The tape was removed, dipped in a solution of iron acetocarmine, and the pollen grains were counted under the microscope. The figures reported in this paper are the mean number of pollen grains collected in an area of 5 cm² each day. The experiment was replicated twice and the data were statistically analyzed for split plot design.

Result and Discussion

The number of pollen grains trapped at various levels and distances was checked in the four directions. Maximum pollen load was observed towards east and minimum towards south of the pollen source. Pollen count was higher in southern direction compared with that of northern and western direction. This was due to western and north western winds which prevailed during the days the experiment was conducted.

The pollen grains were greater near the pollen source. As the distance of pollen source increased, the pollen load decreased. The number of pollen grain at spike level towards east was 9.99, whereas, at the ground level, they were 25.55. On an average, the pollen grain which fell on the ground were almost double then the pollen grains available at spike level. This was true at all the directions and distances. It indicates that wheat pollen is quite heavy and it does not travel to any great distance. JENSEN (1968) reported that 90% of the wheat pollen remained within 20 feet of its source and much of it dropped to the ground within 5 ft. The results, ontained in the present study support the findings of JENSEN (1968). Thus, in the crossing block of hybrid seed production of wheat, fewer male sterile rows would be desirable for adequate seed setting.

(Received October, 1973)