Increasing grove productivity is the new rage among avocado farmers, and appropriately so. One of the main techniques being considered is cross-pollination, an ancient technique, now being recycled. Though we at the Nursery have been lukewarm about benefits from cross pollination experiences with Pinkerton have stirred our interest.

Pinkerton, a variable producer depending on its location, has been exhibiting extraordinary fecundity in the proximity of various Mexican and Mexican x Guatemalan hybrid varieties. These outstanding blocks have produced very large crops in 75-80% of the years we've observed them. Other blocks, interplanted only with Hass (Guatemalan), have produced smaller crops.

Pinkerton is a special variety in several ways, one of its most unusual features being that it blossoms in late fall and continues to produce serial crops of fertile flowers into May. This prolonged blossoming period would seem to provide the variety with cross-pollination opportunities that transcend the individual blossoming periods of other varieties. As everybody knows, most Mexican varieties blossom earlier than most Guatemalan varieties, and the hybrids are intermediate. All of these overlap with Pinkerton's blossoming season.

A second tentative observation is that proximity and abundance of pollinizing material is important. We've a Mexican seed orchard planted close to some Pinkertons which most years bear enormous crops for the size of the trees. Further, we topworked a Pinkerton over to Walter Hole (Mexican). During a year of generally poor Pinkerton set; the Pinkerton nurse limb left on the tree was heavily loaded with fruit.

Another observation influences our thoughts. The periodic winter temperature variations are different from one year to the next. This may be a source of bearing variability for any single variety. Fuerte bearing, for instance, seems to be related to temperatures during the variety's fertile period. When temperature averages are low, insect flights are scant and it may be that pollen tube growth is negatively affected. On the strength of these ideas we've begun to topwork our existing orchards with various candidate pollinizers which represent both Mexican and hybrid types. We hope to take maximum advantage of the long blossoming period of Pinkerton and hope that at least part of its fertile period will be blessed with favorable weather so that we can harvest favorable crops in nearly all years. During these years we hope to purchase isozyme analyses that will genetically identify our most favorable pollinizers.

We have a few guesses of what to expect:

a) Depending upon weather, different pollinizers will be most effective in different years.

b) Depending upon the previous Pinkerton crop, which will affect Pinkerton's blossoming period, different pollinizers will be most effective in different years.

c) Depending upon the solarization of the planted Pinkerton block, pollinization benefits will vary. That's to say that if they are in shaded locations we will have lighter crops.

Anecdotal evidence offered by Roger Essick indicates that Pinkerton set is augmented by Zutano. Meanwhile, we will be trying a similar approach with Hass. Outstanding work by Tom Markle with Gwen and Zutano indicates that some of the points noted above may be operating with Gwen, also. At UCR where multiple varieties are in the vicinity, huge crops of Gwens are recorded.