Sex dimorphism in dioecious Palmer amaranth (Amaranthus palmeri) in response to water stress

Main conclusion Phenological isolation can potentially reduce seed output and may be exploited as a novel tool for ecological management of dioecious weeds. Abstract Dioecious plants may benefit from a maximized outcrossing and optimal sex-specific resource allocation; however, this breeding system may also be exploited for weed management. Seed production in dioecious species is contingent upon the co-occurrence and co-flowering of the two genders and can be further disturbed by flowering asynchrony. We explored dimorphism in secondary sex characters in Amaranthus palmeri, and tested if reproductive synchrony can be affected by water stress. We have used seeds of A. palmeri from California, Kansas and Texas, and studied secondary sex characters under natural conditions and in response to water stress. Seeds of A. palmeri from California (CA) and Kansas (KS) were cordially provided by Dr. Anil Shrestha (California State University, Fresno, California) and Dr. Dallas E. Peterson (Kansas State University, Manhattan, Kansas), respectively. Seeds of a third population were collected from mature plants (about 30 plants) from a set-aside field in College Station, Texas. A. palmeri showed no sexual dimorphism with regard to the timing of emergence, plant height, and relative growth rate. While the initiation of flowering occurred earlier in males than females, females preceded males in timing of anthesis. Water stress delayed anthesis in males to a greater extent than females increasing the anthesis mismatch between the two sexes by seven days. Our data provide the first evidence of environment-controlled flowering asynchrony in A. palmeri. From a practical point of view, phenological isolation can potentially reduce seed output and may be exploited as a novel tool for ecological management of dioecious weeds.

Prevalence of Puccinia abrupta var. partheniicola and its impact on Parthenium hysterophorus in Kathmandu Valley, Nepal

Background Partheniumhysterophorus is a noxious invasive weed in tropical and subtropical regions of the world, including Nepal. Among 11 species of biological control agents released to control P. hysterophorus in Ausrtalia, winter rust Puccina abrupta var. partheniicola arrived fortuitously and has established in Kathmandu Valley, Nepal, nearly a decade back. However, the prevalence and effectiveness of this rust as a biological control agent in Kathmandu remain unknown. To address this knowledge gap, a roadside survey was done at an interval of 2 ± 0.25 km in Kathmandu Valley to assess the P. abrupta var. partheniicola incidence and its impacts on P. hysterophorus. Infested individuals of P. hysterophorus were further divided into four severity classes (very low, low, medium, and high), and rust incidence was calculated. The impact of the winter rust on the growth of P. hysterophorus was assessed by comparing biomass and seed output of infested and non-infested individuals. Results Among 81 locations where P. hysterophorus was present in the Kathmandu Valley, winter rust infestation was observed at 98% locations. At some locations within Kathmandu Valley such as Tinkune, Kirtipur, Chabahil, Buddha Chowk, and Dhobighat, the impacts of the rust on P. hysterophorus were medium to high. Aboveground biomass and seed output of P. hysterophorus were reduced by 47% and 73%, respectively, due to winter rust infestation. The study indicates that winter rust incidence is widespread in Kathmandu Valley with very low to high levels of damages to P. hysterophorus depending on the localities. Conclusion The rust has, therefore, a potential to reduce the growth performance of P. hysterophorus, and it can be used as a component of integrated management of P. hysterophorus by introducing to other suitable areas in Nepal.

Crops and the seed mass-seed output trade-off in plants

A trade-off between seed mass (SM) and seed output (SO) defines a central axis of ecological variation among plants, with implications for understanding both plant trait evolution and plant responses to environmental change. While an observed negative SM-SO relationship is hypothesized to reflect universal constraints on resource allocation in all plants, domestication has likely fundamentally altered this relationship. Using a dataset of SM and SO for 41 of the world most widespread crops and 1,190 wild plant species, coupled with observational data on these traits in soy (Glycine max) and maize (Zea mays), I show that domestication has systematically rewired SM-SO relationships in crops. Compared to wild plants, virtually all crops express a higher SM for a given SO; this domestication signature is especially prominent in seed crops, and also influences the phylogenetic signal in SM and SO. In maize these traits have become positively related likely due to simultaneous selection for greater SM and SO, while in soy these traits have become decoupled likely due to primary selection for SM only. Evolved relationships between SM and SO in plants have been disrupted by both conscious and unconscious artificial selection, which represents a key aspect of how the functional biology of crops differ fundamentally from wild plants along “universal” plant trait spectra.

Contribution to the knowledge of three Indian Spermacoce L. (Rubiaceae) and some preliminary information about their pollination ecology

Se han descrito caracteres taxonómicos no documentados para Spermacoce hispida L. y Spermacoce articularis L. S. hispida es bimórfica. Las flores son débilmente protándrica, nectaríferas y auto-polinizadoras. Las mariposas, las abejas y los trips son importantes como polinizadores. El conjunto de fruta natural más elevado que se evidencia en estas especies se atribuye a autopolinización y entomofilia. Los frutos la dehiscencia es septicida en S. hispida y S. articularis, y circunscisa en Spermacoce pusilla Wall. La dispersión de las semillas es anemo-, baro-, ombro- e hidrocórica. Estas especies ocupan diferentes hábitats para evitar la competencia por los polinizadores y maximizar la producción de semillas y ampliar su rango de distribución. Undocumented taxonomic characters have been described for Spermacoce hispida L. and Spermacoce articularis L. S. hispida is bimorphic. The flowers are weakly protandrous, nectariferous and self-pollinating. Butterflies, bees and thrips are important as pollinators. The highest natural fruit set evidenced in these species is attributed to auto-selfing and entomophily. Fruits dehisce septicidally in S. hispida and S. articularis and circumscissile mode in Spermacoce pusilla Wall. Seed dispersal is anemo-, baro-, ombro- and hydro-chorous. These species occupy different habitats to avoid competition for pollinators and maximize seed output and expand their distribution range.

New Record of Seed Pest, Alcidodes sp. indet. (Coleoptera : Curculionidae) in Cynometra beddomei Prain.- An Endemic, Endangered Legume Tree of the Southern Western Ghats

The weevil, Alcidodes sp. indet (Coleoptera: Curculionidae) was found infest the seeds of Cynometra beddomei, an endemic and endangered legume tree of the Southern Western Ghats. The biology of Alcidodes sp. was studied. The larvae were ‘C’ shaped, measuring 9-10 mm in length, white in colour and found feeding inside the seed for a period of 20-25 days, while the pupal period lasted for 10-15 days. The adults were stout, elongate, oval and black in colour with light brown stripes. The seed infestation estimated to 80% in a fruit year of the tree later severely affected the seed output, germination, seedling emergence followed by the population reduction of species in situ. The incidence of Alcidodes sp. indet on Cynometra beddomei was found to be a new record to the species.