Apple replant disease (ARD) has led to severe yield and quality reduction in the apple industry.  Fusarium solani (F. solani) has been identified as one of the main microbial pathogens responsible for ARD.  Auxin (indole-3-acetic acid, IAA), an endogenous hormone in plants, is involved in almost all plant growth and development processes and plays a role in plant immunity against pathogens.  Gretchen Hagen3 (GH3) is one of the early/primary auxin response genes.  The aim of this study was to evaluate the function of MdGH3-2 and MdGH3-12 in the defense response of F. solani by treating MdGH3-2/12 RNAi plants with F. solani.  The results show that under F. solani infection, RNAi of MdGH3-2/12 inhibited plant biomass accumulation and exacerbated root damage.  After inoculation with F. solani, MdGH3-2/12 RNAi inhibited the biosynthesis of acid-amido synthetase.  This led to the inhibition of free IAA combining with amino acids, resulting in excessive free IAA accumulation.  This excessive free IAA altered plant tissue structure, accelerated fungal hyphal invasion, reduced the activity of antioxidant enzymes (SOD, POD and CAT), increased the reactive oxygen species (ROS) level, and reduced total chlorophyll content and photosynthetic ability, while regulating the expression of PR-related genes including PR1, PR4, PR5 and PR8.  It also changed the contents of plant hormones and amino acids, and ultimately reduced the resistance to F. solani.  In conclusion, these results demonstrate that MdGH3-2 and MdGH3-12 play an important role in apple tolerance to F. solani and ARD.

Sugars are important energy source and signaling molecule in plant, and sugar transporters such as SWEET (sugars will eventually be exported transporters) play important roles in plant growth and development as well as biotic and abiotic stresses.  In this study, a gene named MdSWEET17 was isolated from apple (Malus×domestic).  Expression analysis suggested that MdSWEET17 expressed in all tested tissues (root, stem, leaf, flower and fruit) and the transcript levels were different.  Furthermore, MdSWEET17 transgenic tomatoes and wild type were treated with drought.  The results showed transgenic lines had higher drought tolerance and accumulated more fructose.  Taken together, these findings indicated that MdSWEET17 take part in drought stress response and the regulation of fructose.

Straw mulching allows for effective water storage in dryland wheat production.  Finding a suitable straw mulching model that facilitates wheat growth was the objective of this study.  A 2-year field experiment was conducted to investigate the effects of two straw mulching patterns (FM, full coverage within all the rows; HM, half coverage within alternate rows) and two mulching rates (4.5 and 9.0 t ha^–1) on soil moisture, soil temperature, grain yield, and water use efficiency (WUE) of winter wheat in northern China, with no mulching (M0) as the control.  Results showed that mulching increased the soil water storage in all growth stages under high mulching rates, with a stronger effect in later growth stages.  Water storage under the HM model was greater in later stages than under the FM model.  Soil water content of HM groups was higher than that of FM groups, especially in surface soil layers.  Evapotranspiration decreased in mulched groups and was higher under high mulching rates.  Aboveground biomass during each growth stage under the HM model was higher than that under M0 and FM models with the same mulched rate, leading to a relatively higher grain yield under the HM model.  Mulching increased WUE, a trend that was more obvious under HM9.0 treatment.  Warming effect of soil temperature under the HM pattern persisted longer than under the FM model with the same mulching rates.  Accumulated soil temperature under mulched treatments increased, and the period of negative soil temperature decreased by 9–12 days under FM and by 10–20 days under HM.  Thus, the HM pattern with 9.0 t ha^–1 mulching rate is beneficial for both soil temperature and water content management and can contribute to high yields and high WUE for wheat production in China.