Drought stress is a devastating natural disaster driven by the continuing intensification of global warming, which seriously threatens the productivity and quality of several horticultural crops, including pear.  Gibberellins (GAs) play crucial roles in plant growth, development, and responses to drought stress.  Previous studies have shown significant reductions of GA levels in plants under drought stress; however, our understanding of the intrinsic regulation mechanisms of GA-mediated drought stress in pear remains very limited.  Here, we show that drought stress can impair the accumulation of bioactive GAs (BGAs), and subsequently identified PbrGA2ox1 as a chloroplast-localized GA deactivation gene.  This gene was significantly induced by drought stress and abscisic acid (ABA) treatment, but was suppressed by GA₃ treatment.  PbrGA2ox1-overexpressing transgenic tobacco plants (Nicotiana benthamiana) exhibited enhanced tolerance to dehydration and drought stresses, whereas knock-down of PbrGA2ox1 in pear (Pyrus betulaefolia) by virus-induced gene silencing led to elevated drought sensitivity.  Transgenic plants were hypersensitive to ABA, and had a lower BGAs content, enhanced reactive oxygen species (ROS) scavenging ability, and augmented ABA accumulation and signaling under drought stress compared to wild-type plants.  However, the opposite effects were observed with PbrGA2ox1 silencing in pear.  Moreover, exogenous GA₃ treatment aggravated the ROS toxic effect and restrained ABA synthesis and signaling, resulting in the compromised drought tolerance of pear.  In summary, our results shed light on the mechanism by which BGAs are eliminated in pear leaves under drought stress, providing further insights into the mechanism regulating the effects of GA on the drought tolerance of plants.

Double-seed sowing (two seeds per hole) is the dominant pattern of peanut sowing in China, but within-hole plant competition usually limits their growth and yield formation.  Besides, the traditional double-seed sowing method does not facilitate mechanization during sowing.  The objective of this study was to determine if single-seed sowing at a proper seeding rate yielded better than traditional double-seed sowing pattern and the differences of physiological metabolism of roots.  A field experiment was conducted in two consecutive years to compare pod yields of single-seed sowing at 180 000 (S180), 225 000 (S225), and 270 000 seeds ha^–1 (S270) with that of double-seed sowing at 270 000 seeds ha^–1 (D270) using a completely randomized block design with four replications.  And the root bleeding sap rate, nutrient content, and the main hormone contents in root bleeding sap were also comparatively investigated.  Although the pod yields of single-seed sowing at the three densities were higher than that of traditional double-seed sowing (D270), S225 yielded better than the other two single-seed sowing treatments (S180 and S270).  The increased pod yield in single-seed sowing at 225 000 seeds ha^–1 was mainly due to the higher pod dry weight per plant and harvest index.  The improved pod dry weight and shoot growth had closely relationship with the enhanced root physiological traits such as the increased root bleeding sap rate, content of free amino acids, soluble sugars, K⁺, Mg^2+, Zn²⁺, and Ca²⁺ of the individual plant root.  The improved activity of root reductive, nitrate reductase (NR) and ATPase and higher zeatin and zeatin riboside (Z+ZR) content of root bleeding sap were also crucial to the pod and shoot growth of peanut.  Single-seed sowing at a moderate seeding rate (S225) is a potential practice to increase pod yield and to save seed cost.

 

Hybrid wild boar husbandry is an important component of livestock production in Northeast China.  However, the current disease situation of these animals is largely unknown due to a lack of disease surveillance.  The present study was conducted to determine the prevalence of several important viral diseases in the hybrid wild boar population of Northeast China.  Between September 2015 to December 2016, 169 blood and 61 tissue samples were collected from apparently healthy hybrid wild boars from farms in Jilin, Inner Mongolia and Heilongjiang provinces.  ELISA detected serum antibodies against classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV), pseudorabies virus (PRV), porcine circovirus type 2 (PCV2) and Japanese encephalitis virus (JEV), but not against African swine fever virus (ASFV), with PCV2 having the highest seropositive rate (87.2–100% in different farms).  RT-PCR or PCR performed on the processed samples detected only PCV2, with 33.1% (56/169) of blood samples and 32.8% (20/61) of spleen samples being positive, respectively, indicating widespread PCV2 infection in hybrid wild boars.  Phylogenetic analysis of 15 PCV2 ORF2 sequences showed that they belong to genotypes PCV2a, PCV2b and PCV2d, with nucleotide and deduced amino acid homologies of 88.5–100% and 88.1–100%, respectively.