Citrus canker is a quarantined disease, severely harming citrus plants. Soil beneficial arbuscular mycorrhizal fungi (AMF) can provide a biological control pathway to resist pathogens. This work was to test changes of signal substances including hydrogen peroxide (H2O2), nitric oxide (NO), calmodulin (CaM), salicylic acid (SA) and jasmonic acid (JA) and the pathogen defense gene expression in roots of AMF (Paraglomus occultum) and non-AMF trifoliate orange (Poncirus trifoliata) seedlings after infected by a expressions citrus canker pathogen (Xanthomonas axonopodis pv. Citri, Xac). AMF inoculation significantly improved plant height, stem diameter and leaf number. Xac infection dramatically decreased root H2O2, NO, and SA levels, but increased root CaM and JA concentrations in non-AMF seedlings. There were higher H2O2 and CaM levels and lower JA levels in Xac-infected seedlings than in non-Xac-infected seedlings under mycorrhization. Under non-Xac infection, mycorrhizal treatment reduced root H2O2, NO, and SA but increased CaM and JA levels. However, under Xac infection, mycorrhizal inoculation distinctly accelerated root H2O2, NO, CaM, and SA accumulation, accompanied with up-regulated expression levels of root PtEPS1 (enhance pseudomonas susceptibility 1) and PtPR4 (pathogenesis related gene 4), indicating that Xac stimulated mycorrhizal roles in enhancing resistance of citrus canker. Such results imply that citrus plants with pre-inoculated AMF had stronger resistance to Xac infection through increasing signal substrate accumulation and pathogen defense gene expressions. ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********

The walnut cultivar ‘Yunxin No. 14’ is an early fruiting, high-yielding, and widely adaptable fruit tree with compact growth and superior nuts. Establishing a successful tissue culture system for this cultivar is crucial for its rapid clonal propagation and as a foundation for future genetic transformation. Using young fruits as explants, 3% NaClO sterilization for 20 min effectively controlled contamination and browning. Somatic embryos induced from zygotic embryos cultured on DKW medium with 30 g·L⁻¹ sucrose showed high proliferation and minimal browning. After a 4-day dehydration treatment using saturated NH₄NO₃, mature somatic embryos germinated rapidly on differentiation medium (DKW containing 1 mg·L⁻¹ 6-BA and 0.1 mg·L⁻¹ IBA), reaching 90.0% germination. Optimal shoot multiplication was achieved on DKW medium supplemented with 2 mg·L⁻¹ 6-BA and 0.3 mg·L⁻¹ IBA, yielding a proliferation rate of 91.1% and a proliferation index of 3.1. For rooting, shoots (~3 cm) treated with Clonex^® rooting gel were transferred to a low-cost, sugar-free vermiculite medium with gaseous CO₂ as the sole carbon source. Root initiation occurred within two weeks at a rate of 54.2%, significantly shortening the rooting phase. Rooted plantlets were acclimatized in a peat:perlite:vermiculite (2:2:1, v/v/v) mixture under high humidity for two weeks before outdoor transfer, achieving an 88.6% survival rate. This study provides a reliable protocol for the micropropagation of ‘Yunxin No. 14’ and a valuable reference for other difficult-to-root woody species.

How to improve plant tolerance and yield under salt stress is critical for ensuring sufficient food supply since plant survival and agricultural productivity are both affected by salinity. Some evidence has showed that beneficial microorganisms have a high ability to improve plant salt tolerance and increase crop yield. But few studies were involved in effects of halotolerant yeasts on plants under salt stress. In this present research, Meyerozyma guilliermondii, a halotolerant yeast, was inoculated with tomato plants followed by salt treatment of four different NaCl concentrations (0, 100, 200, and 300 mM). Our results showed that inoculation of M. guilliermondii increased the chlorophyll biosynthesis and photosynthetic machinery effectiveness under salt stress, contributing to biomass accumulation. Under salt treatment of 300 mM NaCl, the yeast inoculation significantly increased ascorbate concentrations in leaves, yet showed no effects on levels of glutathione and proline. Antioxidant enzymes were affected differently by the yeast inoculation. It was found that the yeast inoculation increased superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities under 300, 100, and 200 mM NaCl, respectively. Total soluble sugar levels increased in inoculated tomato plant leaves; however, there were no significant differences between different NaCl concentrations. Under 300 mM NaCl, the yeast inoculation significantly decreased H2O2 levels and reduced malondialdehyde levels. All together, our results showed that halotolerant yeast M. guilliermondii inoculation might be a strong candidate for regulating tomato growth under salt stress by increasing ability to scavenge reactive oxygen species and chlorophyll intactness, and by strengthening photosynthetic machinery.