Population Diversity of Puccinia graminis is Sustained Through Sexual Cycle on Alternate Hosts

A high degree of virulence diversity has been maintained in the population of Puccinia graminis f. sp. tritici （Pgt） in northwestern United States. Although Berberis vulgaris is present in the region and Pgt has been isolated from aecial infections on B. vulgaris, the population is too diverse to be explained by the limited presence of B. vulgaris alone. Since 2008, we have isolated P. graminis from aecial infections on fruits of Mahonia repens and Mahonia aquifolium from northwestern United States. These two native woody shrub species, widely distributed in western North America, were once classified as resistant to P. graminis based on artificial inoculations. By isolating P. graminis from aecia, we established that M. repens and M. aquifolium along with B. vulgaris （albeit infrequent） serve as the alternate hosts ofP. graminis in the region. The isolates of P. graminis from Mahonia of North America had diverse virulence patterns and most of the isolates could be differentiated on Morocco, Line E, Chinese Spring, Little Club, LMPG-6, Rusty, and other genotypes that are considered to be universally susceptible to most Pgt isolates. This discovery explained the persistence of virulence diversity of Pgt observed in isolates derived from uredinia on cereal crops in the region. In addition to cereal crops, uredinial stage of the P. graminis population is sustained by wild grasses, especially Elymus glaucus, a native grass sharing the same habitat with the rusted Mahonia spp. Although virulence to some important stem rust resistance genes was observed in some isolates derived from Mahonia of North America when tested against single stem rust resistance gene stocks, the overall virulence is very limited in these isolates. This is likely a result of limited selection pressure on the rust population. In contrast to northwestern United Sates, the Pgt population in east of the Rocky Mountains of North America has declined steadily with a single race, QFCSC, being predominant in the last decade. This decline is likely due to a combination of factors, of which a lack of sexual recombination in the region is perhaps the most important one.

Identification of eight Berberis species from the Yunnan-Guizhou plateau as aecial hosts for Puccinia striiformis f.sp.tritici,the wheat stripe rust pathogen

Puccinia striiformis Westend.f.sp.tritici Erikss.(Pst)infects wheat and causes stripe rust.The rust is heteroecious with wheat as the primary uredinial and telial host and barberry(Berberis spp.)as the alternate pycnial and aecial host.More than 40 Berberis species have been identified as alternate hosts for Pst,and most of these are Chinese Berberis species.However,little is known about Berberis species or their geographic distributions in the Yunnan-Guizhou plateau in southwestern China.The Yunnan-Guizhou plateau is considered to be an important and relatively independent region for the evolution of the wheat stripe rust pathogen in China because the entire disease cycle can be completed within the region.In this study,we conducted a survey of barberry plants in the Yunnan-Guizhou plateau and identified the eight Pst-susceptible Berberis species under controlled conditions,including B.julianae,B.tsienii,B.veitchii,B.wilsonae,B.wilsonae var.guhtzunica,B.franchetiana,B.lepidifolia and B.pruinosa.These species are reported here for the first time to serve as alternate hosts for the wheat stripe rust pathogen under controlled conditions.

Survey and examination of the potential alternative hosts of Villosiclava virens, the pathogen of rice false smut, in China

Rice false smut is caused by ascomycete Villosiclava virens, whose potential alternative hosts have been assumed previ- ously. Here its potential alternative hosts were surveyed and identified from 2008 to 2013 in the main rice-growing regions in China. Two common weeds in paddy fields, Digitaria sanguinalis Scop. and Echinochloa crusgalli （L.） Beauv., were found to present the similar symptoms to smut diseases in a few individuals in 2012 and 2013 in Zhejiang and Sichuan provinces of China, respectively. After the examinations of the spore morphology, their infection and extension mode in hosts, pathogen cell wall components, and molecular identification, the two pathogens were identified to be the Basidiomycetes, Ustilago syntherismae and Ustilago trichophora, respectively. So far there has been no alternative host of V. virens to be identified in China. These suggest that the alternative hosts of V. virens, if they do exist, are not possible to play an important role in the pathogen life cycle and the disease epidemics.

Alternative Host Plants of Calidea panaethiopica (Hemiptera: Scutelleridae) and Aphtona whitfieldi (Coleoptera: Chrysomelidae), Insect Pests of Jatropha curcas, South Burkina Faso

Jatropha curcas is subject to the attacks of many insect pests, including Calidea panaethiopica Kirkaldy 1909 (Hemiptera: Scutelleridae) whose larvae and adults feed on flowers, fruit and seeds of the shrub resulting in quantitative and qualitative losses;the shrub is also attacked by Aphthona whitfieldi Bryan (Coleoptera: Chrysomelidae) which feeds on the leaves causing complete defoliation in severe attack. Despite their economic importance, very little is known about the alternative host plants of these insect pests. The study of the ecology of these species is a pre-requisite for the development of appropriate control methods. The identification of alternative host plants of C. panaethiopica and A. whitfieldi was conducted from June 3rd 2013 to November 30th 2014 in the Sissili province, South Burkina Faso. During that period, four J. curcas’ plantations of six locations in the province were prospected for alternative host plants of the two insect pests. In each plantation, observations were done across a diagonal up to 500 m away from the plantation. Fallows in the vicinity of the J. curcas plantations were particularly examined. Potential host plants of the two insect pests were collected and bred in the laboratory in Léo where they were used to feed the insect pests. Only Jatropha gossypiifolia, a cousin of J. curcas, was found to be a common alternative host plant of both insect pests.

Alternative Host Plants of <i>Calidea panaethiopica</i>(Hemiptera: Scutelleridae) and <i>Aphtona whitfieldi</i>(Coleoptera: Chrysomelidae), Insect Pests of <i>Jatropha curcas</i>, South Burkina Faso

Jatropha curcas is subject to the attacks of many insect pests, including Calidea panaethiopica Kirkaldy 1909 (Hemiptera: Scutelleridae) whose larvae and adults feed on flowers, fruit and seeds of the shrub resulting in quantitative and qualitative losses;the shrub is also attacked by Aphthona whitfieldi Bryan (Coleoptera: Chrysomelidae) which feeds on the leaves causing complete defoliation in severe attack. Despite their economic importance, very little is known about the alternative host plants of these insect pests. The study of the ecology of these species is a pre-requisite for the development of appropriate control methods. The identification of alternative host plants of C. panaethiopica and A. whitfieldi was conducted from June 3rd 2013 to November 30th 2014 in the Sissili province, South Burkina Faso. During that period, four J. curcas’ plantations of six locations in the province were prospected for alternative host plants of the two insect pests. In each plantation, observations were done across a diagonal up to 500 m away from the plantation. Fallows in the vicinity of the J. curcas plantations were particularly examined. Potential host plants of the two insect pests were collected and bred in the laboratory in Léo where they were used to feed the insect pests. Only Jatropha gossypiifolia, a cousin of J. curcas, was found to be a common alternative host plant of both insect pests.

Physiological Age Status of Female Adults and Off-Season Survival of Rice Leaffolder Cnaphalocrocis medinalis in India

Rice leaffolder, Cnaphalocrocis medinalis, is one of the major foliage feeders found in the rice growing regions in India. When the crop was at maturity, numerous adults of rice leaffolder were found in the rice fields though the larval population gradually decreased, and no eggs were found on rice leaves. The population characteristics of C. medinalis were assessed based on the physiological age status of adults at different crop growth stages. Based on egg development within ovarioles, ovariole appearance number and colour of fat bodies, and characteristics of bursa copulatrix, physiological age status of the adults was described, which served as a basis for the determination of age composition. C. medinalis adults were found during the first week of August on rice plants, of which 44% were in Age 0 with immature ovaries, indicating immigrants. However, 28% adults each were at Ages 1-2 with developing ovaries, indicating local breeding population. The carryover and off-season survival of C. medinalis were also studied to determine the contribution of the alternative hosts in the population growth that helped in devising efficient management strategies. Rice was the most preferred host followed by Triticum aestivum, Echinochloa crusgulli and Brachiaria plantaginea. Various routes of the carryover of C. medinalis from season to season were discussed.

Large-scale gene expression reveals different adaptations of Hyalopterus persikonus to winter and summer host plants

Host alternation, an obligatory seasonal shifting between host plants of distant genetic relationship, has had significant consequences for the diversification and success of the superfamily of aphids. However, the underlying molecular mechanism remains unclear. In this study, the molecular mechanism of host alternation was explored through a large-scale gene expression analysis of the mealy aphid Hyalopterus persikonus on winter and summer host plants. More than four times as many unigenes of the mealy aphid were significantly upregulated on summer host Phragmites australis than on winter host Rosaceae plants. In order to identify gene candidates related to host alternation, the differentially expressed unigenes of H. persikonus were compared to salivary gland expressed genes and secretome of Acyrthosiphon pisum. Genes involved in ribosome and oxidative phosphorylation and with molecular functions of heme-copper terminal oxidase activity, hydrolase activity and ribosome binding were potentially upregulated in salivary glands of//. persikonus on the summer host. Putative secretory proteins, such as detoxification enzymes （carboxylesterases and cytochrome P450s）, antioxidant enzymes （peroxidase and superoxide dismutase）, glutathione peroxidase, glucose dehydrogenase, angiotensin-converting enzyme, eadherin, and calreticulin, were highly expressed in H. persikonus on the summer host, while a SCP GAPR-I-like family protein and a salivary sheath protein were highly expressed in the aphids on winter hosts. These results shed light on phenotypic plasticity in host utilization and seasonal adaptation of aphids.