Human-Mediated Gene Flow Contributes to Metapopulation Genetic Structure of the Pathogenic Fungus Alternaria alternata from Potato.

Metapopulation structure generated by recurrent extinctions and recolonizations plays an important role in the evolution of species but is rarely considered in agricultural systems. In this study, generation and mechanism of metapopulation structure were investigated by microsatellite assaying 725 isolates of Alternaria alternata sampled from potato hosts at 16 locations across China. We found a single major cluster, no isolate-geography associations and no bottlenecks in the A. alternata isolates, suggesting a metapopulation genetic structure of the pathogen. We also found weak isolation-by-distance, lower among than within cropping region population differentiation, concordant moving directions of potato products and net gene flow and the highest gene diversity in the region with the most potato imports. These results indicate that in addition to natural dispersal, human-mediated gene flow also contributes to the generation and dynamics of the metapopulation genetic structure of A. alternata in China. Metapopulation structure increases the adaptive capacity of the plant pathogen as a result of enhanced genetic variation and reduced population fragmentation. Consequently, rigid quarantine regulations may be required to reduce population connectivity and the evolutionary potential of A. alternata and other pathogens with a similar population dynamics for a sustainable plant disease management.

Population genetic analysis reveals cryptic sex in the phytopathogenic fungus Alternaria alternata.

Reproductive mode can impact population genetic dynamics and evolutionary landscape of plant pathogens as well as on disease epidemiology and management. In this study, we monitored the spatial dynamics and mating type idiomorphs in ~700 Alternaria alternata isolates sampled from the main potato production areas in China to infer the mating system of potato early blight. Consistent with the expectation of asexual species, identical genotypes were recovered from different locations separated by hundreds of kilometers of geographic distance and spanned across many years. However, high genotype diversity, equal MAT1-1 and MAT1-2 frequencies within and among populations, no genetic differentiation and phylogenetic association between two mating types, combined with random association amongst neutral markers in some field populations, suggested that sexual reproduction may also play an important role in the epidemics and evolution of the pathogen in at least half of the populations assayed despite the fact that no teleomorphs have been observed yet naturally or artificially. Our results indicated that A. alternata may adopt an epidemic mode of reproduction by combining many cycles of asexual propagation with fewer cycles of sexual reproduction, facilitating its adaptation to changing environments and making the disease management on potato fields even more difficult.

[The status of protein intake and energy supply in the early life of very/extremely low birth weight infants].

OBJECTIVE: To study the relationship of protein intake and energy supply with the physical growth in very/extremely low birth weight infant at their early life. METHOD: Retrospective survey was performed in Neonatal Intensive Care Unit (NICU) in Peking University First Hospital. Inclusion criteria were preterm infant, birth weight < 1500 g, hospitalization for longer than 2 weeks, discharge with body weight greater than 1800 g. The infants were divided into two groups according to gestational age (GA). GA < 32 weeks and ≥ 32 weeks. Physical growth and its relation with the protein intake and energy supply were analyzed. The predictive value of serum blood urea nitrogen (BUN) on protein intake was studied. RESULT: Ninety-three very/extremely low birth weight infants were involved, 69 in GA < 32 weeks group and 24 in GA ≥ 32 weeks group.Compared with GA ≥ 32 group, GA < 32 weeks preterm infants had more weight loss, (9.2 ± 4.4)% vs. (5.0 ± 3.1)%, P = 0.000; slower birth weight recovery (10.6 ± 3.8) d vs. (7.1 ± 2.6) d, P = 0.000; poorer weight gain at 1, 4, 5 weeks of life, (-4.5 ± 9.3) g/ (kg·d) vs. (3.4 ± 6.9) g/ (kg·d), P = 0.000 , (13.5 ± 7.3) g/ (kg·d) vs. (19.2 ± 4.9) g/ (kg·d), P = 0.001, (14.6 ± 5.6) g/ (kg·d) vs. (18.2 ± 4.5) g/ (kg·d), P = 0.031; less energy supply at 1 to 5 weeks (P value was 0.000,0.000,0.025,0.001,0.008 respectively) and less protein intake at 1, 4, 5 weeks of life (P value was 0.009,0.006,0.032). Extrauterine growth retardation (EUGR) was still predominant in our subjects, 47.8% in GA < 32 weeks group, and 95.8% in GA ≥ 32 weeks group, P = 0.000. The incidence increased greater in GA < 32 weeks infants, 43.5% vs. 20.8%, P = 0.000.The duration of weight loss and mechanical ventilation correlated negatively with weight gain rate, respectively ß = -0.591, P = 0.000 and ß = -0.281, P = 0.005; the average energy supply and time taken to reach full enteral feeding were factors improving weight gain, respectively ß = 0.202, P = 0.021 and ß = 0.354, P = 0.000. After birth, serum BUN declined gradually. Positive relation showed between average protein intake at 3(rd) week and BUN level at the end of 3 weeks, r = 0.420, P = 0.000. Serum BUN 1.44, 1.49 mmol/L at the end of 3(rd) and 4(th) week were cut-off predictors for protein intake less than 3 g/(kg·d) at related period, sensitivity and specificity were 65.3%, 83.3% and 60%, 80% respectively. CONCLUSION: No enough protein intake and energy supply, poor weight gain are critical problems in the management of very/extremely low birth weight infants. Prevention from NEC, appropriate parenteral/enteral nutrition transforming will benefit their physical growth. Low serum BUN after 3 weeks of life is a valuable predictor of low protein intake.

Early growth of preterm infants with prolonged hospitalisation.

INTRODUCTION: This study aimed to determine the early growth patterns of preterm infants who required prolonged hospitalisation in terms of body weight Z-score, and to explore the influencing factors and predictors of their growth. METHODS: The criteria of enrolment included preterm birth, singleton pregnancy, hospitalisation within the first 24 hours of life, hospital stay ≥ 28 days and clinical follow-up beyond 91 days of corrected age. Body weight Z-scores and the incidence of underweight infants were reviewed periodically, and the influencing factors and possible predictors of growth analysed. RESULTS: Body weight Z-scores of all infants of gestational age (GA) groups kept decreasing, with a trough seen at 36 weeks corrected gestational age (CGA). At corrected full-term, body weight Z-scores for all birth weight groups achieved birth level and were higher than that at 36 weeks CGA. Body weight Z-scores at 61 days corrected age was (-0.300 × GA [weeks] + 0.210 × birth weight [g] + 0.682 × body weight Z-score) at 40 weeks CGA. The cut-off values for body weight Z-score at birth (cut-off, -1.79; sensitivity, 100%; specificity, 91.3%) and 61 days corrected age (cut-off, -1.95; sensitivity, 100%; specificity, 97.1%) were selected to predict the risk of being underweight at 183 days corrected age. CONCLUSION: Early growth restriction is a practical problem in preterm infants with prolonged hospitalisation. Body weight Z-scores at 40 weeks CGA and 61 days corrected age can be used to predict body weight gain prior to 183 days corrected age in these infants.

[Dynamic evaluation on body weight gain in premature infants and its significance].

OBJECTIVES: To investigate the incidence of intra- and extrauterine growth retardation (EUGR) and growth restriction in premature infants, and to illustrate the growth pattern of them in postnatal and infantile period. METHODS: All premature infants were admitted to our neonatal intensive care unit (NICU) during the recent 7 years. The criteria for enrollment were (1) gestational age < 37 weeks; (2) single fetus; (3) admitted within the first 24 hours of life; (4) hospitalization period ≥ 14 days; (5) clinical follow-up persisted till ≥ 3 months of corrected gestational age. Intrauterine growth restriction (IUGR), EUGR and growth restriction were defined as having a measured growth value (weight) that was ≤ 10(th) percentile of Chinese infants' growth curve in corrected age on admission, discharge and follow-up period. Results were analyzed by using SPSS 12.0 statistical software package by chi-square test, rank-sum test, and t test. RESULTS: Two hundred and thirty nine infants were involved, 134 were boys and 105 girls. The incidence of IUGR and EUGR assessed by weight was 25.5% and 40.6%, respectively. The lower the birth weight was, the higher the incidence of IUGR and EUGR was. The percentile of body weight in the growth curve at discharge was lower than that at birth (Z = -7.784, P = 0.000). The incidence of growth restriction assessed by weight was 20.5%, 15.0%, 8.8%, 17.0%, 10.4%, 10.1%, 11.9%, 7.0% at corrected gestational age of 38 - 40 weeks, corrected age of 28 d, 61 d, 91 d, 122 d, 152 d, 183 d, and 274 d, respectively. The incidences of growth restriction were stable when the corrected age was older than 91 days. The incidence of growth restriction in female premature infants at 183 days' corrected age was higher than that in male children (χ(2) = 6.181, P = 0.017), the incidence was 19.3% and 3.8% respectively. During the follow-up period, most of the average body weight of premature infants whose gestational age was < 32 weeks or birth weight ≤ 1500 g were lower than the 50(th) percentile of the growth curve except the average body weight of boys whose gestational age < 32 weeks at corrected age of 2 and 4 months. CONCLUSIONS: Premature and/or low birth weight infants are at high risk of growth restriction, especially very low birth weight infants. The incidence of growth restriction decreased with growth. Long-term prognosis requires further investigation.