Fruit Tree Biotechnology Programme
Westfalia Technological Services and FABI have established a collaborative joint venture to complement the research objectives of a sustainable avocado breeding program. The specific research requirement focuses on the understanding of disease tolerance/resistance of avocado rootstocks against Phytophthora cinnamomi to facilitate the development of superior avocado rootstocks.
The Souh African avocado industry expanded steadily from the early 1970s to 2003, with plantings of +-2000 ha in 1970 increasing to +-12 000 ha in 2003. Growth in plantings, however, has slowed since 2003 with total area planted to commercial avocado orchards remaining stable at around 12 000 ha. 'Hass' and 'Fuerte' are the major cultivars each accounting for 37% of the area under avocados.
Approximately 70% of the trees produced by avocado nurseries are 'Hass' and the remaining 30% is comprised mostly of 'Fuerte', 'Ryan' and 'Pinkerton'. Avocado nurseries are currently producing ca. 110 000 trees p.a. These trees are mainly being used to replace old orchards, but there are also some completely new orchards being planted.
Phytophthora cinnamomi is the one of the most important limiting factors in avocado production in most avocado-producing countries. It attacks all varieties of avocado which results in the death of the tree. In South Africa root rot of avocado is the most important avocado disease (Kremer-Kohne & M L Mukhumo, 2003). Currently, the South African avocado industry relies on chemical control of root rot with phosphite compounds integrated with practices that promote root health, such as the addition of compost and mulches and the use of rootstocks which is moderately tolerant to root rot. However, the majority of plantings since the early 1980s have been on Phytophthora- tolerant rootstocks such as 'Duke 7', and in recent years a growing number of trees on the rootstock 'Merensky II (Dusa) have been planted. Approximately 60% of current nursery trees are on 'Merensky II'. Although the disease has been studied for more than 60 years, definite control measures have not been found and losses continue to mount. Phytophthora root rot is becoming an increasing threat to the sustainable production of avocados for many growers (Coffey, 1987).
Westfalia Technological Services has provided the world avocado industry with a superior new rootstock. This rootstock has tolerance against Phytophthora cinnamomi and is presently the best performing rootstock in terms of Hass yielding and tree health. Although Westfalia have a selection of tolerant/resistant mother trees, the exact mode of resistance is not known. A clear understanding of disease resistance is therefore essential to facilitate the breeding or development of resistant/tolerant avocado rootstocks. Westfalia Technological Services outsourced this project to FABI under the management of a dedicated University based senior researcher.
The search for genes conferring resistance to diseases and pests has become an important objective towards understanding plant resistance and developing genetically improved agricultural crops. Little is however known about the molecular processes underlying resistance responses, metabolic pathways and downstream signaling of the avocado- Phytophthora cinnamomi (Pc) interaction. An analysis of pathogen-induced genes will lead to a better understanding of the molecular processes involved in resistance, and will contribute to the development of biotechnological strategies to combat the disease and develop tolerant/resistant plant material.