The root, a key organ for sensing the soil environment, is easily damaged by environmental stresses such as low soil temperature. Although the exact mechanism is unknown, exogenous sucrose can mitigate the oxidative damage to the root caused by low temperatures in the root zone. In this study, we examined how exogenous sucrose affected the transcriptome and physiology of Malus baccata Borkh. seedling roots at sub-low root-zone temperature (LRT). The exogenous sucrose treatment was more effective than other treatments in mitigating LRT stress injury. This was achieved by decreasing reactive oxygen species (O 2 .- and H2O2) 2 O 2 ) and malondialdehyde content, increasing the activities of antioxidant enzymes (SOD, POD, CAT, APX, GR, and MDHAR), increasing AsA and GSH content, and increasing soluble sugar content. Transcriptome analysis revealed that alpha-linolenic acid metabolism, fatty acid biosynthesis, phenylpropane biosynthesis, and glycolysis/gluconeogenesis were the primary areas of enrichment for the differentially expressed genes identified under the LRT treatment. Exogenous sucrose may enhance the tolerance of Malus baccata Borkh. to LRT by regulating the expression of differentially expressed genes ( GST, LOX, SS, PFK, ADH, , and 4CL) ) related to the antioxidant system, carbohydrate metabolism, alpha-linolenic acid metabolism, and phenylpropane biosynthesis pathways. These results offer a foundation for additional investigation into the molecular mechanism underlying the modulation of the root response to low temperature by exogenous sucrose.

The root-lesion nematode, Pratylenchus penetrans, is a ubiquitous parasite of roots of temperate fruit trees. It affects early growth of trees replanted into former orchard sites where populations have built up and may contribute to decline complexes of older trees. Most British Columbia, Canada, apple acreage is planted with M.9 rootstock, but growers are increasingly considering Geneva-series rootstocks such as G.41 and G.935. Among these rootstocks, responses to P. penetrans, specifically, are poorly known. To compare the resistance and tolerance to P. penetrans of G.41, G.935, and M.9 rootstocks ('Ambrosia' scion), a field microplot experiment was established in spring of 2020 at the Summerland Research and Development Centre. The experimental design was a two by three factorial combination of: P. penetrans inoculation (+/-) and rootstock (G.41, G.935, and M.9), with 20 replicate microplots of each of the six treatment combinations arranged in a randomized complete block design. The P. penetrans inoculum was 5,400 nematodes per microplot (54 P. penetrans liter-1 soil), which is below commonly accepted damage thresholds. Though P. penetrans population densities were lower for the G.41 rootstock by the end of the 2021 growing season, the effects of P. penetrans were similar among rootstocks. In the establishment year (2020), P. penetrans caused significant reductions in aboveground growth. In 2021, shoot growth and root weight were reduced by P. penetrans. The nematode also reduced rates of leaf gas exchange and stem water potential. These data suggest that while G.41 and G.935 may have other horticultural benefits over M.9, they are equally susceptible to P. penetrans at the early stages of tree growth.