Transcriptomics reveal the genetic coordination of early defense to Armillaria root rot (ARR) in Prunus spp.

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.

IBA Delivery Technique and Media Salts Affected In Vitro Rooting and Acclimatization of Eight Prunus Genotypes.

Difficult-to-root plants often perform poorly during acclimatization and in vitro rooting can increase the survival and quality of plants. The influence of auxin application and mineral nutrition on in vitro rooting and subsequent effects on plant quality in eight Prunus genotypes were investigated. Microshoots were rooted in vitro on Murashige and Skoog (MS), ½ MS, Driver and Kuniyuki (DKW), or New Prunus Medium (NPM) media formulations in combination with 15 µM indole-3-butyric acid (IBA), 4-day 15 µM IBA pulse, 1 mM 30 s quick-dip, or IBA-free treatments. Shoots were observed pre- and post-acclimatization to determine rooting methods to maximize quality and minimize labor. A genotype-specific response to auxin application was observed with seven of eight genotypes achieving 100% survival when paired with the recommended IBA treatment. Peaches performed best when treated with 4-day IBA pulse or 30 s quick-dip. Rooting of P. cerasifera, it's hybrid to P. persica, and P. munsoniana all benefitted from IBA application. Shoots rooted with 15 µM IBA were smaller and lower quality in most genotypes. DKW maximized size and quality in six genotypes. Better shoots and larger root systems during in vitro rooting produced better plants in the greenhouse with no detrimental effect of callus growth. Rooting techniques to maximize plant quality while reducing labor are specified.

An In Vitro Co-Culture System for Rapid Differential Response to Fusarium oxysporum f. sp. vasinfectum Race 4 in Three Cotton Cultivars.

Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4) is a devastating fungus pathogen that causes Fusarium wilt in both domesticated cotton species, Gossypium hirsutum (Upland) and G. barbadense (Pima). Greenhouse and field-based pathogenicity assays can be a challenge because of nonuniform inoculum levels, the presence of endophytes, and varying environmental factors. Therefore, an in vitro coculture system was designed to support the growth of both domesticated cotton species and FOV4 via an inert polyphenolic foam substrate with a liquid medium. A Fusarium wilt-susceptible Pima cotton cultivar, G. barbadense 'GB1031'; a highly resistant Pima cotton cultivar, G. barbadense 'DP348RF'; and a susceptible Upland cotton cultivar, G. hirsutum 'TM-1', were evaluated for 30 days during coculture with FOV4 in this foam-based system. Thirty days after inoculation, disease symptoms were more severe in both susceptible cultivars, which displayed higher percentages of foliar damage, and greater plant mortality than observed in 'DP348RF', the resistant Pima cotton cultivar. This foam-based in vitro system may be useful for screening cotton germplasm for resistance to a variety of fungus pathogens and may facilitate the study of biotic interactions in domesticated cotton species under controlled environmental conditions.

Correction to: In vitro mineral nutrition of Curcuma longa L. affects production of volatile compounds in rhizomes after transfer to the greenhouse.

Following publication of the original article [1], the author reported a formatting error and an error in the figure caption. The original article has been corrected. The details of the errors are as follows.

In vitro mineral nutrition of Curcuma longa L. affects production of volatile compounds in rhizomes after transfer to the greenhouse.

BACKGROUND: Turmeric is a rich source of bioactive compounds useful in both medicine and cuisine. Mineral concentrations effects (PO43-, Ca2+, Mg2+, and KNO3) were tested during in vitro rhizome development on the ex vitro content of volatile constituents in rhizomes after 6 months in the greenhouse. A response surface method (D-optimal criteria) was repeated in both high and low-input fertilizer treatments. Control plants were grown on Murashige and Skoog (MS) medium, acclimatized in the greenhouse and grown in the field. The volatile constituents were investigated by GC-MS. RESULTS: The total content of volatiles was affected by fertilizer treatments, and in vitro treatment with Ca2+ and KNO3; but PO43- and Mg2+ had no significant effect. The content was higher in the high-input fertilizer treatments (49.7 ± 9 mg/g DM) with 4 mM Ca2+, 60 mM KNO3 and 5 mM NH4+, than the low-input fertilizer (26.6 ± 9 mg/g DM), and the MS control (15.28 ± 2.7 mg/g DM; 3 mM Ca2+, 20 mM K+, 39 mM NO3-, 20 mM NH4+, 1.25 mM PO43-, and 1.5 mM Mg2+). The interaction of Ca2+ with KNO3 affected curcumenol isomer I and II, germacrone, isocurcumenol, and ß-elemenone content. Increasing in vitro phosphate concentration to 6.25 mM increased ex vitro neocurdione and methenolone contents. CONCLUSION: These results show that minerals in the in vitro bioreactor medium during rhizome development affected biosynthesis of turmeric volatile components after transfer to the greenhouse six months later. The multi-factor design identified 1) nutrient regulation of specific components within unique phytochemical profile for Curcuma longa L. clone 35-1 and 2) the varied phytochemical profiles were maintained with integrity during the greenhouse growth in high fertility conditions.

Micropropagation, Acclimatization, and Greenhouse Culture of Veratrum californicum.

Micropropagation and production of Veratrum californicum is most successful when using a premixed Murishage and Skoog basal medium with vitamins and a 5-week subculture cycle at 16 °C for multiplication. These culture conditions provide the best percent survival after acclimatization in the greenhouse. However, clone response to temperature and light quality within culture conditions varies. Micropropagated plants have mass and morphology similar to 2- or 3-year-old seedlings. Acclimatized plantlets can then be grown in the greenhouse using sub-irrigation (ebb and flood) to maintain substrate volumetric water content > 44 %. Growth cycle in the greenhouse must be about 100 days, followed by dormancy for 5 months at 5 °C.

In vitro growth of Curcuma longa L. in response to five mineral elements and plant density in fed-batch culture systems.

Plant density was varied with P, Ca, Mg, and KNO3 in a multifactor experiment to improve Curcuma longa L. micropropagation, biomass and microrhizome development in fed-batch liquid culture. The experiment had two paired D-optimal designs, testing sucrose fed-batch and nutrient sucrose fed-batch techniques. When sucrose became depleted, volume was restored to 5% m/v sucrose in 200 ml of modified liquid MS medium by adding sucrose solutions. Similarly, nutrient sucrose fed-batch was restored to set points with double concentration of treatments' macronutrient and MS micronutrient solutions, along with sucrose solutions. Changes in the amounts of water and sucrose supplementations were driven by the interaction of P and KNO3 concentrations. Increasing P from 1.25 to 6.25 mM increased both multiplication and biomass. The multiplication ratio was greatest in the nutrient sucrose fed-batch technique with the highest level of P, 6 buds/vessel, and the lowest level of Ca and KNO3. The highest density (18 buds/vessel) produced the highest fresh biomass at the highest concentrations of KNO3 and P with nutrient sucrose fed-batch, and moderate Ca and Mg concentrations. However, maximal rhizome dry biomass required highest P, sucrose fed-batch, and a moderate plant density. Different media formulations and fed-batch techniques were identified to maximize the propagation and storage organ responses. A single experimental design was used to optimize these dual purposes.