Per H. McCord

Species-specific detection and identification of fusarium species complex, the causal agent of sugarcane pokkah boeng in China.

Background Pokkah boeng disease caused by the Fusarium species complex results in significant yield losses in sugarcane. Thus, the rapid and accurate detection and identification of the pathogen is urgently required to manage and prevent the spreading of sugarcane pokkah boeng. Methods A total of 101 isolates were recovered from the pokkah boeng samples collected from five major sugarcane production areas in China throughout 2012 and 2013. The causal pathogen was identified by morphological observation, pathogenicity test, and phylogenetic analysis based on the fungus-conserved rDNA-ITS. Species-specific TaqMan real-time PCR and conventional PCR methods were developed for rapid and accurate detection of the causal agent of sugarcane pokkah boeng. The specificity and sensitivity of PCR assay were also evaluated on a total of 84 isolates of Fusarium from China and several isolates from other fungal pathogens of Sporisorium scitamineum and Phoma sp. and sugarcane endophyte of Acremonium sp. Result Two Fusarium species (F. verticillioides and F. proliferatum) that caused sugarcane pokahh boeng were identified by morphological observation, pathogenicity test, and phylogenetic analysis. Species-specific TaqMan PCR and conventional PCR were designed and optimized to target their rDNA-ITS regions. The sensitivity of the TaqMan PCR was approximately 10 pg of fungal DNA input, which was 1,000-fold over conventional PCR, and successfully detected pokkah boeng in the field-grown sugarcane. Conclusions/Significance This study was the first to identify two species, F. verticillioides and F. proliferatum, that were causal pathogens of sugarcane pokkah boeng in China. It also described the development of a species-specific PCR assay to detect and confirm these pathogens in sugarcane plants from mainland China. This method will be very useful for a broad range of research endeavors as well as the regulatory response and management of sugarcane pokkah boeng.

The Incidence and Effect on Total Tuber Carotenoids of a Recessive Zeaxanthin Epoxidase Allele (Zep1) in Yellow-fleshed Potatoes

Zeaxanthin epoxidase (Zep) is one of at least two genes important for the incidence and amount of carotenoids in yellow-fleshed potato. The recessive allele of the gene encoding zeaxanthin epoxidase (Zep1) has previously been shown to inhibit the conversion of the xanthophyll zeaxanthin to other, more polar carotenoids. We examined the effect of the dosage of Zep1 on total carotenoids in yellow-fleshed tetraploid potato germplasm. The dosage of heterozygous individuals was determined using high-resolution DNA melting. We also surveyed a wide range of germplasm available in the USDA-ARS potato breeding program in Washington for the presence and dosage of Zep1. Genotypes with zero, one, or two copies of Zep1 had statistically similar levels of total tuber carotenoids. Triplex individuals showed a small but significant increase in total carotenoids over the previous three classes. In turn, individuals that were homozygous for Zep1 had much higher levels of total carotenoids than all other dosage classes. This suggests that a slight dosage effect is present, but that the effect of Zep1 is indeed largely recessive. A significant amount of variation in total carotenoids was observed within all Zep1 dosage classes, reinforcing the evidence that additional loci are important for high total carotenoids in potato. Our survey of breeding germplasm supported earlier research that Zep1 is uncommon in tetraploid potato germplasm. The use of high-resolution DNA melting again allowed us to identify the dosage of Zep1 in heterozygous individuals. This is important for breeding high-carotenoid potatoes at the tetraploid level, since recovery of homozygous Zep1 individuals is very rare. Identification of agronomically desirable parents with two or more copies of Zep1 would allow for higher recovery of homozygous Zep1 progeny, permitting additional selection for other desirable traits.ResumenZeaxantina epoxidasa (Zep) es uno de por lo menos dos genes importantes para la incidencia y cantidad de carotenoides en papa de pulpa amarilla. Se ha mostrado previamente que el alelo recesivo del gene que codifica a la Zeaxantina epoxidasa (Zep) inhibe la conversión de xantofila zeaxantina a otros carotenoides menos polares. Examinamos el efecto de la dosis del alelo recesivo Zep, en carotenoides totales en germoplasma de papa tetraploide de pulpa amarilla. Se determinó la dosis de individuos heterozigotes usando la desnaturalización de alta resolución de ADN. También estudiamos una gran amplitud de germoplasma disponible en el programa de mejoramiento de papa USDA-ARS en Washington, para la presencia y dosis de Zep recesivo. Los genotipos con cero, una o dos copias de Zep recesivo tenían estadísticamente niveles similares de carotenoides totales de tubérculo. Los individuos con tres copias mostraron un incremento pequeño, pero significativo, en carotenoides totales, sobre las tres clases previas. Por otro lado, los individuos que fueron homozigotes para Zep recesivo tuvieron niveles más altos de carotenoides totales que todas las otras clases de dosis. Esto sugiere que esta presente un efecto ligero de dosis, pero que el efecto de Zep es, de hecho, grandemente recesivo. Se observó una cantidad significativa de variación en carotenoides totales dentro de todas las clases de dosis de Zep, reforzando la evidencia de que loci adicionales son importantes para altos carotenoides totales en papa. Nuestro estudio del germoplasma de mejoramiento respaldó investigación previa en que Zep recesivo es poco común en germoplasma tetraploide de papa. El uso de la desnaturalización de alta resolución de ADN nuevamente nos permitió identificar la dosis de Zep recesivo en individuos heterozigóticos. Esto es importante para el mejoramiento de papas con alto carotenoide a nivel de tetraploides, considerando que es muy rara la recuperación de individuos homozigóticos recesivos de Zep. La identificación de padres agronómicamente deseables con dos o más copias de Zep recesivo permitirá alta recuperación de progenie homozigota recesiva de Zep, facilitando una selección adicional para otros caracteres deseables.

Character association and selection indices in sugarcane.

Sugarcane is an important crop of Khyber Pakhtunkhwa province of Pakistan. However, the yield per unit area is below some advanced sugarcane growing areas of the world, and the national average of Pakistan. Improved methods of selection resulting in higher yielding sugarcane cultivars would help in increased yield. Information about direct and indirect effects of yield contributing characters and subsequently developing a selection index would greatly improve the process of cultivar development. An experiment comprising 26 sugarcane genotypes coupled with 2 check cultivars was grown in a randomized complete block design with 3 replications at Sugar Crops Research Institute, Mardan, Pakistan during 2011-2013. Data were collected on stalk and yield attributes. Genotypic path coefficients revealed that Tiller2, growth2, and Pol had positive direct effects on cane yield. Selection indices based on growth2, Pol, tiller2, and cane yield showed that individuals selected based on these characters simultaneously gave a genetic advance of above 60. CPF-225, MS-2003-CR5-245, MS-2003-CR7-243, and MS-2003-CR8-407 could be selected as the best genotypes according to these selection indices. This study showed that applying path coefficient analyses followed by development of selection index could be a worthwhile selection strategy.

Albinism in Sugarcane: Significance, Research Gaps, and Potential Future Research Developments

The usefulness of breeding to improve sugarcane (Saccharum sp. hybrids) crop performance and productivity depends heavily on the continued availability of new and beneficial genes and on novel approaches to the reproductive and agronomic controls used to access their full potential. One such novel approach is perhaps in the study of full or partial (variegation) albinism, an underexplored topic with implications both in sugarcane cultivar development and crop production. In sugarcane and other domesticated cereal grasses, cell culture (e.g., anther, callus, and immature embryo culture) has been employed via haploid and diploid embryogenesis in order to obtain genetically favorable parents, though rates of albinism in the regenerated plantlets are significantly high and remain a major bottleneck. The rate of photosynthesis in sugarcane leaves is known to throttle down throughout the growing season, and there is evidence that sink availability provides strong feedback. How an albino tiller—a genuine photosynthate sink—will accumulate sugar and biomass and respond to light cues and senescence, as well as how the rest of the plant will respond to an albino tiller, is currently unknown. In this short communication, we discussed the significance, critical gaps, and potential future developments of albinism in sugarcane research.

Sugarcane genotype performance in three environments (based on crop cycle) at Mardan, Pakistan.

Sugarcane breeders often face significant genotype x environment interactions in their trials grown under multiple environments. Hence, genotypes need to be tested for their stability across different environments keeping in view the significant interactions. An experiment comprising 28 sugarcane genotypes (including 2 checks) was planted in two plant and one ratoon crops during 2010 to 2013 in a randomized complete block design with 3 replications. Data were recorded on cane, yield, and quality characters. Analyses of variance showed significant mean squares for crops, genotypes, and their interactions. The linear contrasts of two plant crops were found non-significant for tillering, vigor rate, stalk diameter, Brix, Pol, recovery, and cane yield. However, the contrast for plant crops versus ratoon was non-significant for stalk diameter only. Shukla’s stability variances and yield stability indices (Ysi) showed that no single genotype was stable for all characters. However, genotypes MS-2003-CP-209, MS-2003-CP-275,CoJ-76, MS-2003-CR2-131, and MS-2003-CR5-245 were stable for cane yield. The results of the study indicate the Original Research Article American Journal of Experimental Agriculture, 4(3): 362-375, 2014 363 importance of genotype x environment interaction and stability in the ongoing varietal development program.