Phytophthora resistance in cacao (Theobroma cacao): Influence of pod morphological characteristics

Abstract

Twelve diverse cacao (Theobroma cacao) genotypes were assessed for pod resistance to Phytophthora palmivora at the penetration and post-penetration stages of infection using two inoculation methods. Correlation analysis between a number of pod characteristics (stomatal frequency, stomatal pore length, surface wax, thickness of exocarp/endocarp, hardness of exocarp/mesocarp, moisture content) and resistance indicated a strong relationship between resistance to lesion establishment (lesion frequency) and the joint effect of stomatal frequency and pore length. The epidermal impressions of the pod surfaces bearing germinating zoospores of P. palmivora provided evidence that penetration occurs through stomata, epidermal hair base, scar and by direct penetration. A poor correlation was obtained between the pod characteristics studied and post-penetration resistance, suggesting that this resistance, assessed by lesion size, is not governed by morphological or physical characteristics of the pod, but probably by biochemical factors. The importance of these findings in breeding of cacao for resistance to P. palmivora is discussed.

Testing local cocoa selections in Sulawesi: (ii) resistance to stem canker and pod rot (black pod) caused by Phytophthora palmivora

“…3) are consistent with observations of this clone in East Java (Agung Susilo) and the previously reported performance of the parental clone Sca 12 (Iwaro et al, 1997a). However, the field resistance recorded in ICCRI04 was not confirmed by artificial inoculation (Fig.…”

“…Similarly, Ppr incidence was positively correlated with lesion expansion following inoculation ( Table 2), suggesting that susceptibility to the initiation of new infections (which would need to overcome pre-penetration resistance mechanisms) was related to susceptibility to lesion expansion at the post-penetration stage of infection. Resistance to P. palmivora common to stems and pods, and leaves and pods, in individual genotypes has been previously reported (see Iwaro et al, 1997a). In the present study, correlation tests between canker and Ppr (whether naturally occurring or induced artificially) did not support a relationship between resistance in pods and stems in either trial (see Results 3.3).…”

Usefulness of the Detached Pod Test for Assessment of Cacao Resistance to Phytophthora Pod Rot

“…The accessions were categorised into 7 groups ( Figure 1) based on the frequency and spread of the established lesions. According to Iwaro et al (1997a), the frequency and spread of lesions following infection of the pod by Phytophthora are likely to be governed by different resistance mechanisms. Such information will facilitate recombination of genes for the two forms of resistance in new cacao varieties.…”

Transcriptional Profiling of Rapidly Growing Cucumber Fruit by 454-Pyrosequencing Analysis

“…Each sample was measured for five neighboring consecutive cells to obtain mean cell size and were observed at three locations by light microscope at 100· magnification with acridine orange dye (0.1 mgÁmL -1 ). Impressions of intact 8 and 16 DPP epidermal tissues were prepared for microscopy by applying a thin layer of clear nail polish to the fruit surface as was described in Iwaro et al (1997).…”