Screening of citrus rootstocks for salt tolerance in semi-arid climates - A review

Abstract

Generally, Citrus species are grown in tropical and sub-tropical climates where the rainfall is limited, so irrigation is required to sustain the plant growth, creating salinity problems. Citrus species are very sensitive to salinity. Salinity affects seed germination, plant growth, fruit yield and it causes nutrient imbalances in the plants. The most harmful constituent of saline soils is NaCl. Under saline conditions, Na+ and Cl- ions increase in the plant and K+ and Mn2+ decrease. To select salt tolerant rootstocks for citrus, screening of germplasm is required. Both in vivo and in vitro techniques have been used for screening. NaCl is the principal salt used for the screening experiments. The plants tolerate salinity either by exclusion or less transportation of Na+ and Cl- to aerial plant parts. Na+, Cl- and Na:K ratio are important chemical markers, which can be used for approximating the salt tolerance in citrus rootstocks. Callus browning can also be considered as an index for screening purposes. Cleopatra mandarin, Rangpur lime, Citrus macrophylla, Sunki mandarin and Shekwasha mandarin are rootstocks tolerant to salinity and rough lemon and trifoliate orange are sensitive. However, variation in salt tolerance exists among the strains of various citrus rootstocks.