Genetic Variation for Resistance to Phytophthora Root Rot in Eastern White Pine Seedlings

John Frampton,Anne Braham,Martin Pettersson

doi:10.3390/f9040161

Abstract

Deployment of genetically resistant Eastern white pine (Pinus strobus L.) planting stock could reduce economic losses to root rot caused by Phytophthora cinnamomi Rands in Christmas tree and forest plantations. This study aimed to determine the degree of genetic control of resistance to P. cinnamomi in Eastern white pine and secondarily, to compare the aggressiveness of two P. cinnamomi isolates derived from different host species. Phytophthora isolates from Fraser fir (Abies fraseri (Pursh) Poir.) and Eastern white pine were used in a main and supplemental study, respectively, including 83 and 20 open-pollinated families. In each study, two-year-old seedlings were inoculated twice each of two consecutive years and mortality was assessed biweekly for 16 weeks each year. During the first year, mortality increased over time to 18.6% and 40.4% while family variation in mortality ranged from 1.3% to 60.0% and 12.5% to 73.0% in the main and supplemental studies, respectively. At the end of the first year, individual-tree and family-mean heritability estimates were, respectively, 0.44 ± 0.0935 and 0.85 ± 0.180 for the main study, and 0.57 ± 0.216 and 0.90 ± 0.343 for the supplemental study. The P. cinnamomi isolate from Eastern white pine was more aggressive and there was a large interaction between isolates and pine families. Deploying resistant families will be complicated by this interaction but should, nevertheless, reduce economic losses.

Highlights

Eastern white pine (Pinus strobus L.) is a coniferous species with a natural range extending from southeastern Canada, through the Midwest and Northeast regions of the United States and southward through the Southern Appalachian Mountains and into adjacent upper Piedmont regions [1]
Initial mortality was observed after six weeks, mortality rapidly increased through the 10-week assessment after which the increase in mortality slowed and peaked at 40.4% in the final assessment
Mortality for the 20 families included in the supplemental study averaged 26.4% in the main study, slightly higher than the average of all 83 families (18.6%) (Table 1, Figure 2)

Summary

Introduction

Eastern white pine (Pinus strobus L.) is a coniferous species with a natural range extending from southeastern Canada, through the Midwest and Northeast regions of the United States and southward through the Southern Appalachian Mountains and into adjacent upper Piedmont regions [1].Commercially, the wood is used for lumber, cabinetry, millwork, and toys. 39,790 ha of Eastern white pine are in timber production [3] and 95% of the volume harvested is grown in the mountainous western region of the state [4]. [1,5] In North Carolina, it has traditionally been grown in the mountains for cut Christmas trees and greenery, growers have extended the range eastward into the Piedmont and Coastal Plain regions. It has traditionally been grown in the mountains for cut Christmas trees and greenery, growers have extended the range eastward into the Piedmont and Coastal Plain regions There, it is grown on ‘choose and cut’ farms and often cultivated with a suite of other species including Eastern white pine is a worthy Christmas tree species with soft blue-green foliage, good post-harvest needle retention, relatively strong branches but only a slight aroma. [1,5] In North

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