Search

In vitro co-culture techniques that allow the growth of plants and pathogens under controlled environmental conditions are being used to re-create host plant infection. These approaches reduce infection times, promote reproducibility, and enable a rapid evaluation of plant-pathogen interactions. As a result, these systems have become essential in breeding programs aimed at developing plant resistance to diseases. In this study, we developed and validated an in vitro co-culture system to investigate the Armillaria root rot (ARR) affecting Prunus spp. This disease, caused by fungi Armillaria spp. and Desarmillaria caespitosa, poses a severe threat to the stone and nut fruit industry due to the susceptibility of most commercial rootstocks to infection and the lack of effective management options for its control. The system consists of a fiber-supported liquid approach in sterile plastic vessels that allows a fast and reproducible fungal infection under controlled environmental conditions. The floor of the vessels was covered with a polyester-fiber matte and a germination paper that served as an interface between the mycelia and the plant roots. The vessels were subjected to inoculation with Armillaria mellea and D. caespitosa, and three Prunus genotypes ('Guardian®', 'MP-29', and Prunus cerasifera '14–4') were co-cultured with both fungi. Disease progression and plant and fungal biomass were monitored during co-culture. The presented in vitro co-culture approach facilitates the concurrent growth of Armillaria/Desarmillaria spp. and Prunus spp., excluding most of the limitations associated with greenhouses and field experiments. This system provides consistent and reproducible conditions for investigating a prominent plant disease affecting Prunus spp. [ABSTRACT FROM AUTHOR]

Armillaria root rot (ARR) poses a significant threat to the long-term productivity of stone-fruit and nut crops in the predominant production area of the United States. To mitigate this issue, the development of ARR-resistant and horticulturally-acceptable rootstocks is a crucial step towards the maintenance of production sustainability. To date, genetic resistance to ARR has been found in exotic plum germplasm and a peach/plum hybrid rootstock, 'MP-29'. However, the widely-used peach rootstock Guardian® is susceptible to the pathogen. To understand the molecular defense mechanisms involved in ARR resistance in Prunus rootstocks, transcriptomic analyses of one susceptible and two resistant Prunus spp. were performed using two causal agents of ARR, including Armillaria mellea and Desarmillaria tabescens. The results of in vitro co-culture experiments revealed that the two resistant genotypes showed different temporal response dynamics and fungus-specific responses, as seen in the genetic response. Gene expression analysis over time indicated an enrichment of defense-related ontologies, including glucosyltransferase activity, monooxygenase activity, glutathione transferase activity, and peroxidase activity. Differential gene expression and co-expression network analysis highlighted key hub genes involved in the sensing and enzymatic degradation of chitin, GSTs, oxidoreductases, transcription factors, and biochemical pathways likely involved in Armillaria resistance. These data provide valuable resources for the improvement of ARR resistance in Prunus rootstocks through breeding. [ABSTRACT FROM AUTHOR]

A disposable, flexible film vessel was demonstrated for liquid culture micrporopagation of Poacea × 'Cape Breeze' and a micropropagation process was optimized for this system. Process factors involving media volume and plant density; mineral factors of ammonium and phosphate concentrations; and the important organic chemicals sucrose and benzyladenine; were simultaneously varied in the presence and absence of an inert paper substrate (40 treatment combinations for the six continuous factors, duplicated for the nominal factor, paper). Plant multiplication was enhanced by having fewest plants per vessel (10) with the largest volume of medium (90 mL), with the greatest concentrations of benyzladenine (10 µM) and phosphate (6.25 mM), in the absence of the paper. Optimal ex vitro growth, measured by dry mass increase on the mist bed required plants that had been grown under very different in vitro conditions (the smallest volume of medium per vessel (30 mL), fewest plants per vessel (10), low benzyladenine (1.6 µM), lowest phosphate (1.25 mM), in the presence of paper). Media that produced the largest in vitro plants produced plants that rapidly increased in dry mass in the greenhouse. Increasing the number of plants per vessel (30) increases the economy of the system with greater numbers of plants, but they are smaller and grow more slowly than the low-density cultures. In a small experiment using 80 vessels, separate optimal conditions in both process and media formulation were determined for both stage II and stage III cultures of Poacea. The analysis identified most important factors that drive the responses, from other significant responses with less impact. Key message: A liquid culture micropropagation system for Poacea in flexible-film vessels was optimized for process and nutritional factors in both stages II and III in a small, response surface method experiment. [ABSTRACT FROM AUTHOR]