UAE Environmental & Agricultural Information Centre

Untitled Document

Virus-free citrus plant production

Abstract

Virus-free of citrus seedlings were produced for many varieties of citrus fruit in the Tissue Culture Labs. Such as shoot tip grafting method and the produced seedlings were proved free of rapid deterioration virus (Tristeza ) by using the Elisa method .

Introduction

Citrus plant are infected by many virus diseases and Tristeza virus which eradicates thousands of citrus trees in various countries especially grafted on bitter orange trees and causing big loss in agricultural economy.
The spread of this virus was clearly shown in different regions of UAE and the percentage of infection was averaged between 1-16% which led to the death of many trees .

The reasons behind the rapid spreading of this disease may refer to the easy way of transmitting by( Myzus citrcidous ),and mechanically through grafting Scissors , agricultural tools and also by grafting from an infected mother trees .
In addition that the phenomenon of incompatibility between the root stock and the graft caused the death of many trees aged between 7-10 years .

To avoid these reasons, the tissue culture method was adopted to produce virus free-of citrus seedling especially Tristeza as well to avoid the incompatibility between the root-stock and the graft in purpose of maintaining the citrus crop, considering the full care of seedlings and conduct periodical spraying for being protected from Myzus citricidous as a carrier of Tristeza virus.

The growing seeds of the root stock in the hatchery

Material and Methods

The technique of virus- free seedling production is based on three phases.

The first phase:

Root stock After sterilization with a dilute of Sodium hydroxide, the seeds of the root stock are planted in a solid medium already prepared containing the necessary salts and vitamins in addition to certain hormones which help in hastening the germination and the growth .Plantation place in test tubes which are incubated in a temperature and humidity regulated incubator for 15-20 days .

Tubes contain the nutrition medium and bitter orange seeds .The resulting plant reached to about 10 cm in length.

The second phase: Micro grafting

This is the stage of grafting of leading buds taken from virus –free citrus trees especially Tristeza virus after being examined through Liza test .
Those are in the planting equipment ( with laminar flow ) and sterilized against any pollutants, then the heading meristem is expected with a microscope .The root stock plant is also prepared by first sterilization and then removed of two third of its stem, then a T shaped is made on the stem and the meristem of the graft is placed inside it and fixed.

This material is again planted with the necessary feeding media in test tubes placed and incubated in the growth chamber at temperature of
28-32 c with 16 hours of illumination daily for 30 days till the graft of the stock is fixed and a plant is formed inside the test- tube .

The third phase: Shoot Tip Grafting

This is the last stage , planting material obtained in the laboratory is transferred to the green house where the final root –stock are kept .

The growing bud is then removed and re grafted on the final root -s tock plant and the whole plant is covered with a plastic bag to raise the humidity .The bag is removed gradually till the plant reaches a size that allows its planting in the open field, considering the periodical irrigation and fertilizing . This way gives a virus-free plant and avoids the occurrence of incompatibility.

Recommendations

Due to the expand in agriculture and planting many varieties of local and imported citrus are planted therefore , we find it necessary to adopt the tissue- culture propagation method in large scales to produce virus- free citrus seedlings in great numbers which are adapted with climate
conditions in UAE .