A homeowner planted three avocado trees on his property, and his are the only avocado trees in his neighbourhood but they are not fruiting. The varieties are Hass, Gwen and Pinkerton, as he is after the flavour and had a aversion to green skinned varieties. The trees were flowering as usual, and the foliage were green and does not show signs of drought stress.
Avocado trees have perfect flowers meaning the male and female parts are in the same flower, so Dendro's assistant was wondering if it could self-pollinate. Dendro explained that the male and female part are not active on the same tree at the same time, a flowering behavior known as synchronous dichogamy. There are two types of varieties: A-varieties that open their flowers as female in the morning and as male in the afternoon, and B-varieties that open their flowers in a vice-versa manner. During the male phase, the stamen is upright and during the female phase, the stamen lays flat around the stigma.
The detectives observed that the client's trees are A-varieties, as their visit was in the afternoon and the stamens are all upright. The three varieties planted by the client were determined to be A-varieties, and cannot fruit without B-varieties around. Dendro explained that more A-varieties are cultivated but B-varieties are necessary to pollination.
Hence, if the client wishes for his trees to bear fruit, he would have to plant B-varieties like Bacon, Fuerte or Zutano. A new breeding program from the University of California is evaluating two new B-varieties - 'Nobel' and 'Marvel' - that produces a black, Hass-like fruit.
Additional reading: Arpaia, M.L., A.E. Fetscher, and R. Hofshi. Avocado Flowering Basics. University of California Agriculture & Natural Resources. http://ucavo.ucr.edu/Flowering/FloweringBasics.html
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