Leaching Soluble Salts Increases Population Densities of Tylenchulus semipenetrans

P. Mashela, L. W. Duncan, J. H. Graham, R. McSorley


The effect of salinity on population densities of Tylenchulus semipenetrans was measured on 3-month-old salt-tolerant Rangpur lime growing on either loamy sand, sand, or organic mix and on 4-month-old salt-sensitive Sweet lime in organic mix. Salinity treatments were initiated by watering daily with 25 mol/m³ NaCl + 3.3 mol/m³ CaCl[sub2] for 3 days and every other day with 50 mol/m³ NaC1 + 6.6 mol/m³ CaC1[sub2] for one week, with no salt (NS) treatments as controls. Salinity was discontinued in one treatment (DS) by leaching with tap water prior to inoculation with nematodes, whereas the continuous salinity (CS) treatment remained unchanged. Overall, in Rangpur lime organic soil supported the highest population densities of T. semipenetrans, followed by loamy sand and sand. The DS treatment resulted in the highest (P = 0.05) mean population densities of T. semipenetrans in the three soil types. Similarly, the DS treatment in Sweet lime resulted in the highest (P = 0.05) nematode populations. The DS treatment predisposed citrus to nematode infection through accumulated salt stress, whereas leaching soluble salt in soil solution offered nematodes a suitable nonosmotic habitat. Nematode females under the DS treatment also had the highest (P = 0.05) fecundity. Key words: Citrus limettioides, citrus nematode, citrus reticulata, electrical conductivity, nematode, Rangpur lime, salinity, soil type, Sweet lime, pH, Tylenchulus semipenetrans.

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