Effects of arbuscular mycorrhizal fungi on resistance to <i>Phytophthora parasitica</i> of citrus seedlings and on growth of Thai honey tangerine scions on citrus rootstocks

Abstract

Thai honey tangerine (Sainamphueng tangerine) is generally grown by grafting on rootstocks of another variety of tangerine or citrus species which may differ in their reaction to beneficial and pathogenic soil organisms. The objectives of this study were to evaluate responses to arbuscular mycorrhizal (AM) fungi and Phytophthora parasitica of different citrus genotypes and the effect of AM fungi on the growth of scions of Thai honey tangerine grafted on different citrus rootstocks including Cleopatra tangerine, lime, pomelo, Swingle citrumelo and Troyer citrange. Significant differences were found among citrus species in the percentage of root colonization by the AM fungi and in the severity of root rot disease when inoculated with P. parasitica alone. Thai honey tangerine was most susceptible and Cleopatra tangerine was most resistant to P. parasitica. Inoculation with AM fungi could reduce disease severity of all the citrus plants from P. parasitica. AM fungi enhanced the growth of seedling to the greatest extent in lime. Variation in the response to AM fungi was found among the scions of Thai honey tangerine on different citrus rootstocks. The scion of Thai honey tangerine grew best on the lime rootstock inoculated with AM fungi.

Key words: Phytophthora parasitica, citrus, rootstock, arbuscular mycorrhizal (AM) fungi, root rot.