Virulence tests of Neofusicoccum parvum, Lasiodiplodia theobromae, and Phytophthora palmivora on Theobroma cacao

Abstract

Neofusicoccum parvum is a recently reported pathogen affecting Theobroma cacao L., and has been isolated from symptomatic pods on Oahu and Hawaii Islands. Determining infection routes and virulence are essential for assessing the impact of N. parvum on cacao production and developing effective disease management strategies. Infection routes were determined by inoculating unwounded stems and pods with six isolates of N. parvum alongside Lasiodiplodia theobromae and Phytophthora palmivora. Fifty percent of unwounded stems inoculated with P. palmivora developed lesions, but only a single lesion developed following inoculation with N. parvum (isolate H44). L. theobromae and the remaining N. parvum isolates did not induce lesion development on unwounded stems. In contrast, all N. parvum and L. theobromae isolates produced lesions on 40–100% of unwounded pods of GNV 164 and GNV 360. Low incidences of infection were observed in unwounded pods of ICS 95 (0–66.7%), SHRS 21 (0–75%), and SHRS 33 (0–20%). On wounded pods, all pathogen species produced similar size lesions, ranging from 1.90 to 7.60 cm four days after inoculation. Results from this study show that all three species can produce high rates of pod infection on some clones in the absence of wounds, but stem infection is less likely. In addition, this is the first report of L. theobromae infecting cacao pods and P. palmivora infecting stems in the absence of wounds.

Fungal Pathogens of Cacao in Puerto Rico

“…Neofusicoccum parvum was found to be a common cause of pod rot on cacao in Hawaii [46,47], but was not detected during this study. This may be due to the warmer climate of Puerto Rico compared with Hawaii, as N. parvum has a lower temperature optimum and range than L. theobromae, which was frequently detected in this study [47]. The related Neofusicoccum mangiferae was detected in a single sample.…”

“…Due to the presence of numerous saprophytes and endophytes in the vascular tissue of T. cacao trees, stem samples underwent an additional step to improve the likelihood of recovering pathogens. Instead of plating tissue directly on media as described above, they were inserted into openings made in healthy 4-month-old cacao pods, placed in zip lock bags, and incubated at room temperature (28 ± 3 • C) as described in Puig et al [47] (Figure 5a). After three days, tissue was sampled from the margins of newly emerging lesions, surface disinfested, and plated on 1 /2 PDA media (Figure 5b) as described above.…”

“…Five-month-old open-pollinated pods of the clone CCN 51 were wounded with a 1 mm diameter probe, to a depth of 2 mm, and 6 mm discs of 1 /2 PDA with actively growing mycelia of each isolate were placed mycelial-side down over the site, covered with a damp 1 × 1 cm 2 filter paper square, and wrapped in parafilm, as described in Puig et al [47]. They were placed in laboratory growth chambers at 25 • C in the dark.…”

Phytophthora theobromicola sp. nov.: A New Species Causing Black Pod Disease on Cacao in Brazil

“…Southeastern Asia is considered the center of diversity of P. palmivora, but it has been found associated with cacao trees worldwide and also being able to infect several wild and cultivated hosts in South America (Wang et al, 2020). Phytophthora palmivora has been reported infecting a broad range of hosts in different botanical families (Zentmyer et al, 1973;Erwin and Ribeiro, 1996;Luz et al, 2001;Puig et al, 2021). In Brazil, this pathogen is infecting Annona squamosa, Bactris gasipaes, Carica papaya, Citrus sp., Cocos nucifera, Ficus carica, Herrania sp., Hevea brasiliensis, Solanum lycopersicum, Piper nigrum, T. cacao, and T. grandiflorum (Erwin and Ribeiro, 1996;Luz et al, 2001;Decloquement et al, 2019;Lopes et al, 2019).…”

Identification of native soil-derived Trichoderma spp. isolates and analysis of their antagonist traits against Lasiodiplodia theobromae causing stem-end rot in papaya

“…Geographically, it can be found almost everywhere around the world, with a higher frequency in tropical and subtropical areas, making it one of the most widely distributed Botryosphaeriaceae species (Phillips et al 2013;Mehl et al 2017). The fungus has been shown to cause pathogenic infection in papaya (Yuan et al 2019), mango (Goudarzi et al 2021, banana (Kulkarni et al 2021), cocoa (Puig et al 2021), cassava (Brito et al 2020) and other tropical fruit plants (Karunanayake and Adikaram 2020). In general, L. theobromae infection causes diseases such as branch dieback, stem cankers, and seed and fruit decay (Netto et al 2014).…”