Comparative Histopathology of Host Reaction Types in Slash Pine Resistant to Cronartium quercuum f. sp. fusiforme

Karina Gramacho,Thomas Miller,Robert Schmidt

doi:10.3390/f4020319

Abstract

Histological examinations of the host reaction types (RTs); short galls, rough galls and smooth galls in slash pine seedlings inoculated with Cronartium quercuum f. sp. fusiforme revealed host reaction zone(s) [RZ(s)]. These RZs differed among the host RTs in location and pattern of occurrence in the stem, staining reaction, periderm formation and amount of fungal colonization. The RZ within short galls were wide, deep in the cortex, continuous around the stem, bordered on both sides by a well-developed periderm encircling the stem with limited fungal colonization. The RZ of the rough galls lacked a periderm, were small, numerous and discontinuous around the stem circumference, being separated by symptomatic tissue typical of a susceptible reaction. Fungal colonization of the rough galls was limited and hyphae and haustoria were encrusted. The RZ of the smooth galls were small and narrow conforming to the stem circumference, shallow in the cortex and interconnected by symptomatic tissues typical of a susceptible reaction. A narrow periderm developed along the innermost portion of the RZ in smooth galls and fungal colonization was abundant in the cortex. We suggest that the RTs large galls (rough and smooth), short galls, and hypersensitive-like stem lesions represent increasing resistance to the fusiform rust pathogen.

Highlights

Fusiform rust of pines, caused by Cronartium quercuum (Berk.) Miyabe ex
The Reaction Zones (RZs) differed in pattern, staining reaction, periderm formation and fungal colonization as summarized in Reaction zone(s)
Reaction zones in slash pine occurred in response to colonization by the fusiform rust pathogen as shown by Miller et al [13], Lundquist and Miller [24] and Jewell et al [16] and by our observation of the reaction types rough, smooth and short galls, which differed in the RZ location, pattern of staining and fungal colonization

Summary

Introduction

Fusiform rust of pines, caused by Cronartium quercuum (Berk.) Miyabe ex. Shirai f. sp. fusiforme, is an important disease of slash [Pinus elliottii (Engelm.) var. elliottii] and loblolly (P. taeda L.) pines.Losses to the disease are severe in intensively managed pine plantations in the southeastern USA [1,2].Deployment of rust-resistant genotypes has substantially reduced fusiform rust incidence and losses in newly established plantations [3,4,5,6,7]. Fusiform rust of pines, caused by Cronartium quercuum (Berk.) Miyabe ex. Fusiforme, is an important disease of slash [Pinus elliottii (Engelm.) var. Elliottii] and loblolly (P. taeda L.) pines. Losses to the disease are severe in intensively managed pine plantations in the southeastern USA [1,2]. Deployment of rust-resistant genotypes has substantially reduced fusiform rust incidence and losses in newly established plantations [3,4,5,6,7]. Selection for resistance to C. quercuum f. Fusiforme was initially assessed by the presence or absence of galls in field trials [8,9] and in shadehouse tests [10,11]. In greenhouse trials on pine seedlings at the Resistance Screening Center, Bent Creek Selection for resistance to C. quercuum f. sp. fusiforme was initially assessed by the presence or absence of galls in field trials [8,9] and in shadehouse tests [10,11].

Objectives

Results

Conclusion