New Zealand and Australia Avocado Grower’s Conference ’05. 20-22 September 2005. Tauranga, New Zealand. Session 7. Flowering, fruit set and yield. 9 pages. THE CALIFORNIA CROSS POLLINATION EXPERIMENT – A PROGRESS REPORT ON THE INFLUENCE OF POLLINIZER VARIETY AND PROXIMITY ON ‘HASS’ YIELD Mary Lu Arpaia, David Stottlemyer, Loretta M. Bates and Eric Focht Department of Botany and Plant Sciences University of California, Riverside, CA 92521 arpaia@uckac.edu, david.stottlemyer@ucr.edu, loretta.bates@ucr.edu, eric.focht@ucr.edu SUMMARY Preliminary results from a pollinizer trial in Oxnard California are reported. Yield data collected from 2002 – 2005 suggest that the presence of pollinizer varieties in close proximity enhance the total number of fruit harvested from ‘Hass’. The influence of pollinizers on yield diminishes as the distance from the pollinizer variety increases. Differences were detected between pollinizer varieties in terms of influencing ‘Hass’ yield. The highest ‘Hass’ yields were observed when ‘Fuerte’, ‘Zutano’ and ‘SirPrize’ were used as the pollinizer. The lowest cumulative yield was observed when ‘Harvest’, an A-Flower type was used. Small but significant differences have been detected in percent dry weight, fruit and seed length/width ratio and seed size. Key words: pollinizer, yield, proximity INTRODUCTION Research dating back to early avocado research has highlighted the importance of understanding the nuances of avocado flowering. However a review of the literature (Gustafson and Bergh, 1966, Davenport, 1986) also shows that this topic still remains controversial regarding the need for pollinators (the vector for pollination), pollinizers (complementary varieties) and strategic placement of pollinizer varieties (Arpaia and Hofshi, 2004, Arpaia et al 2004, Davenport, 2004). Nirody (1922) was the first to describe synchronous dichogamy in the avocado, that is, the occurrence of distinctive female and male stages within an individual flower. Stout in 1923 described this behavior in detail for California avocado varieties and then later for Florida cultivars (1933). He also categorized avocado varieties into A- and B-Flower types. Under normal weather conditions, A-Flower types open as female flowers in the morning of one day; close at mid-day then open in the male stage the following afternoon. The B-Flower types open female in the afternoon of day 1 and reopen in the male stage the following morning. Stout and Savage (1925) were the first to suggest the possible benefit of interplanting varieties with complementary flowering types to enhance overall avocado productivity. Research suggesting the need for a vector to carry the pollen from one flower to the next was also established by pioneer avocado researchers. Clark (1923) in the first caging studies of avocado showed the need for pollen-transferring agent such as honey bees although his caging research also demonstrated that considerable differences