Genetic Tolerance in Capsicum Chinense to Low pH Constraints on Root Growth ^†

Peppers (Capsicum spp.) are valuable cash crops in developing countries of the tropics and sub-tropics where acidic soils represent a substantial amount of arable land. The optimal soil pH for pepper production is about 6.0 to 7.5 and soil acidity causes significant production losses. Soil acidification is aggravated by high inorganic nitrogen fertiliser input which is a critical component in maximising pepper yields. Application of lime can effectively amend the pH but it is a major cost to poor farmers in developing countries. The opportunity to identify pepper genotypes with resistance to low pH can reduce production costs whilst increasing yield.

A glasshouse solution culture experiment was conducted to investigate the effects of pH on root elongation of two commercial cultivars Warlock and Plato (C. annuum) and eight wild chilli accessions (C. chinense). The experimental design was a randomised complete block with six pH treatments (6.0, 5.4, 5.1, 4.8, 4.5 and 4.2) and three replicates. After germinating seeds in a rolled-towel, the plants were transplanted to 30-L plastic containers containing dilute nutrient solution when the average radicle length was 25–40 mm. At 14 days after transplanting the length of the longest root was determined individually. Root elongation was expressed relative to that in the pH 6.0 treatment.

The relative root length of three wild accessions was substantially greater than that of the commercial cultivars at pH 4.8 to 4.2. Two wild accessions had considerably higher mean root lengths than that of Warlock and Plato at pH 4.5 and 4.2.