Increased temperature reduces walnut pollen germination in semi-arid regions of Australia

Walnuts grown in semi-arid production regions of Australia experience high daily temperatures during pistillate and staminate flower bloom. Our aim was to assess the impact that high temperatures have on pollen viability. Samples of partially shed catkins were heat treated at 23 (room), 28, 32, 36 or 40°C for 24 h, after which pollen samples were collected at 0, 24, 48 72 and 96 h. Pollen samples were incubated on growth media (24 h at 27°C) and germination assessed microscopically. Pollen viability decreased with increasing temperature, irrespective of the time-period, with less than 0.5% germination following treatment at 36 and 40°C. Pollen germination was greater at 28 and 32°C than at higher temperatures, although germination reduced over time. Pollen viability did not reduce within 24 h of treatment at 23°C; however, viability reduced from 48 h onwards. Studies examining pollen viability at various temperature and time periods are ongoing.