Association between plant nutrients, the development of Huanglongbing and abnormal growth symptoms in navel orange.

Abstract

Huanglongbing (HLB) causes extensive damage in citrus orchards worldwide. Symptoms include blotchy mottle leaf (BML) and little leaf chlorosis (LLC), and nutrient deficiency usually occurs concurrently. However, the relationship between plant mineral content and infection with Candidatus Liberibacter asiaticus (CLas) is not clearly established. We sampled 7-month-old autumn shoots with three characteristic phenotypes, asymptomatic leaf (AL), BML and LLC, representing HLB disease progression, and further divided samples into CLas-infected and uninfected based on PCR analysis. HLB infection decreased transfer coefficients of Mg and K from leaf to phloem tissues through regulation of the transporter genes Cs3g03790.1 and PtrMGT5, increasing the content of leaf Mg and K. HLB infection also decreased leaf Zn, xylem Ca and phloem Ca and Zn content. Leaf Ca, Mg, Zn and B content decreased while leaf K content increased significantly as symptoms progressed from AL to LLC. The transport of P from leaf to phloem tissue, as evaluated by the transfer coefficient, was regulated by the transporter CsiPT2, resulting in irregular levels of leaf P. Our results provide insights into the nutrient dynamics in Citrus in response to CLas infection and the progression of HLB symptoms.