Proc. of Second World Avocado Congress 1992 pp. 559-562

 

A Study of Avocado Germplasm Resources, 1988 1990. V. The Evaluation of the Collected Avocado Germplasm Material for Horticultural Purposes

 

 

A. Ben-Ya'acov, Miriam Zilberstaine, and I. Sela

ARO, Volcani Center, Bet-Dagan, 50250, Israel

 

 

Abstract. During earlier stages of the research, germplasm was collected in different countries and planted in Israel as a germplasm bank. About 50 representatives of this germplasm bank were propagated vegetatively in 1985 and planted in selected sites under stress conditions. The soils where the experimental orchards were planted have one or more of the following stress factors: salinity, lime, limited aeration, exchangeable sodium, high pH, low fertility and Phytophthora infestation. Vegetative development and health conditions of the trees were surveyed every year. Recently, most of the trees were grafted to a commercial cultivar. The findings collected from the experimental orchards show large differences among germplasm sources when planted as rooted trees.

 

 

Growing conditions for the avocado are worsening at an accelerated rate (salinity, exchangeable Na⁺, Phytophthora cinnamomi infection, etc.). Thus, there is a need to continuously search for stress-tolerant rootstocks (Soderholm, 1981).

This project is a part of an international study of avocado germplasm collected from different countries, mostly areas of origin of the avocado (Ben Ya'acov et al., 1990). The germplasm collected is evaluated in Israel for horticultural purposes.

Materials and Methods

The 54 different rootstocks (Table 1) were propagated clonally and planted in 1985 in orchards at 6 sites in different commercial avocado areas of Israel. Six replicates were planted at each site. The sites are characterized by different stress conditions (Table 2). Two years after planting, the rootstocks were grafted to a commercial variety, usually Wurtz, a dwarf rootstock. Tree growth and development was investigated mainly by using aerial view photography. An annual survey of leaf burn, chlorosis and Phytophthora cinnamomi tolerance, gives us a large number of basic data on each rootstock.

Results

The information collected in the first 5 years includes one year with unusual heat (1988) and one year with severe frost (1989). During these years, four of our grafted clones are growing well in P. cinnamomi-infested soil (Table 3). The outstanding clones 'Day', 'Antigua', 'Galvan', and '256' showed no leaf burn, no degeneration symptoms and have the best growth and development rates. Eight other clones from the germplasm bank were marked as moderate and will be studied more in the future.

In the alkaline soils, 'Mayo 133' has had outstanding resistance. 'VC 257' grew well in salinity and poor aerated soils. Under the severe desert conditions in Gilat, 'Stuart' showed no leaf burn symptoms due to salinity and lime, but exhibited chlorosis. 'Day', 'Antigua¹, 'Galvan¹ and '256' were outstanding clones under the various stress conditions.

Discussion

It is well known that clones differ in their behavior when planted in different ecological conditions. In our study, some of the rooted types are more universal in their adaptation, such as 'Day' and 'Orizaba 3', while others grew well only in one stress environment.

The wide behavioral range of our analyzed rootstocks enables us to select specific stocks for specific stress conditions and even more important than the study of the individual physiological behavior basis for specific resistance mechanisms. Ultimately, we hope to develop a bioassay for rapid screening for a specific resistance.

Literature Cited

Ben-Ya'acov, A., G. Bufler, A. Barrientos, E. De La Cruz Torres, L. Lopez, H. Degani, and A. Solis Molina. 1990. A study of the avocado genetic resources. GIARA Project 1-15.

Soderholm, P.K. 1981. Catalog of plant germplasm available from the Subtropical Horticulture Research Unit, Miami, Florida. Agric. Rev. and Manuals, ARM-S-19.