WINETECH Technical Yearbook 2019

DETECTION AND QUANTIFICATION OF BLACK FOOT DISEASE AND CROWN AND ROOT ROT PATHOGENS IN GRAPEVINE NURSERIES

JULY 2019

SHAUN LANGENHOVEN, FRANCOIS HALLEEN 1 , CHRIS SPIES & LIZEL MOSTERT 2 : 1 ARC Infruitec-Nietvoorbij, Stellenbosch; 2 Department of Plant

Pathology, Stellenbosch University, Stellenbosch KEYWORDS: Black foot disease, crown and root rot.

A B PHOTO 1. Soil samples were taken with an auger. Nursery soils were different as can be seen from a dryer soil (a) versus a more waterlogged soil (b).

The aim of this study was to evaluate the effect of different rotation crops used by nurseries on BFD and CRR pathogens by detecting and quantifying these pathogens in nursery plants and soil. INTRODUCTION Grapevine decline is a disease complex that affects young vines in all grape growing regions of the world and leads to a lower survival rate for young vines. A major contributing factor to grapevine decline is black foot disease (BFD), and crown and root rot (CRR). Studies in South Africa have shown that BFD and CRR pathogens are present in nursery vines as asymptomatic

infections. Black foot disease of grapevines is a serious soilborne disease occurring mainly in nurseries and young vineyards, and are more often encountered at disease clinics (Department of Plant Pathology, SU and ARC Infruitec-Nietvoorbij) than CRR. Black foot disease of grapevines is caused by species of the genera Dactylonectria (previously known as Cylindrocarpon ), Ilyonectria (previously Cylindrocarpon ), Campylocarpon , Cylindrocladiella and Thelonectria . The BFD species are soil inhabitants and are regarded as saprobes and weak pathogens, and infect roots through wounds and natural openings. In

nurseries, the most visible symptoms include plants with reduced vigour, shortened shoots and internodes, sparse foliage and interveinal chlorosis. Upon dissection of the roots and basal ends of rootstocks, black discolouration, gum inclusions of the xylem vessels, and brown vascular streaking can be observed. A reduction in root biomass and root hairs, and sunken necrotic root lesions may also be observed on afflicted plants. In young vines (less than five years old) death can occur rapidly. All BFD pathogens except

Campylocarpon species can produce thick- walled chlamydospores which would allow these pathogens to persist in the soil for long periods. Crown and root rot is caused by species belonging to the genera Phytophthora , Pythium and Phytopythium . Root and crown rot symptoms include black to brown root necrosis, while the above ground plant parts show typical decline symptoms, such as stunted growth, leaf chlorosis, wilting, die- back, poor fruit-set and shoot growth. It