Impact of Seed Transmission on the Infection and Development of Pitch Canker Disease in Pinus radiata

Margarita Evira-Recuenco,Rosa Raposo,Eugenia Iturritxa

doi:10.3390/f6093353

Abstract

The aim of this study was to determine the impact of seed inoculum on subsequent disease development in nurseries, specifically studying incidence of seed infection, transmission rate of seed to seedlings, and rate of disease development from the primary inoculum source. Transmission rate of Fusarium circinatum (F. circinatum) from symptomatic trees of Pinus radiata (P. radiata) to seed was 0.73%, being the fungus mainly on the coat. Seed infection incidence was positively correlated with tree disease severity. Seeds also become contaminated with F. circinatum during storage, where high relative humidity had a great effect regardless of temperature. Transmission rates from seeds to symptomatic seedlings measured at 48 days after seed inoculation with 104 and 106 was 28% and 80%, respectively. Seedlings showed symptoms of wilting and dieback, and eventually died within the total duration of this study (475 days). By this time, there were two remaining symptomless seedlings (1% of the total). F. circinatum was recovered from each of them, demonstrating its persistence in seedlings. Fungus populations in roots were estimated between 105 and 107 cfu/g in symptomatic plants for both inoculum doses and up to 104 cfu/g in asymptomatic plants. Disease infection rate was similar in post-emergence damping-off (up two months growing) and for established seedlings (up to eight months) after seeds were inoculated with 104 spores/mL.

Highlights

Pitch canker disease, caused by Fusarium circinatum (F. circinatum) Nirenberg and O’Donnell, is an emergent disease that is threatening Pinus trees in Europe
F. circinatum was isolated from P. radiata seeds from trees with cankers of pitch canker disease, but at a frequency less than 1%
These results are in agreement with those obtained in routine seed health testing that has been performed in Spain since F. circinatum was detected in 2005, which are very low

Summary

Introduction

Pitch canker disease, caused by Fusarium circinatum (F. circinatum) Nirenberg and O’Donnell, is an emergent disease that is threatening Pinus trees in Europe. Since it was first recognized in Southeastern. USA [1], the disease has been reported in other parts of the world [2] In many of these reports, the disease appeared first in forest nurseries, like in South Africa [3], Chile [4], Spain [5], Portugal [6] and Brazil [7]. The fungus can infect seeds internally, where it causes damage to embryo and gametophyte tissues [13]

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