Image analysis for the automatic phenotyping of Orobanche cumana tubercles on sunflower roots

Background The parasitic plant Orobanche cumana is one of the most important threats to sunflower crops in Europe. Resistant sunflower varieties have been developed, but new O. cumana races have evolved and have overcome introgressed resistance genes, leading to the recurrent need for new resistance methods. Screening for resistance requires the phenotyping of thousands of sunflower plants to various O. cumana races. Most phenotyping experiments have been performed in fields at the later stage of the interaction, requiring time and space. A rapid phenotyping screening method under controlled conditions would need less space and would allow screening for resistance of many sunflower genotypes. Our study proposes a phenotyping tool for the sunflower/O. cumana interaction under controlled conditions through image analysis for broomrape tubercle analysis at early stages of the interaction. Results We optimized the phenotyping of sunflower/O. cumana interactions by using rhizotrons (transparent Plexiglas boxes) in a growth chamber to control culture conditions and Orobanche inoculum. We used a Raspberry Pi computer with a picamera for acquiring images of inoculated sunflower roots 3 weeks post inoculation. We set up a macro using ImageJ free software for the automatic counting of the number of tubercles. This phenotyping tool was named RhizOSun. We evaluated five sunflower genotypes inoculated with two O. cumana races and showed that automatic counting of the number of tubercles using RhizOSun was highly correlated with manual time-consuming counting and could be efficiently used for screening sunflower genotypes at the tubercle stage. Conclusion This method is rapid, accurate and low-cost. It allows rapid imaging of numerous rhizotrons over time, and it enables image tracking of all the data with time kinetics. This paves the way toward automatization of phenotyping in rhizotrons that could be used for other root phenotyping, such as symbiotic nodules on legumes.

Screening for Resistance in Farmer-Preferred Cassava Cultivars from Ghana to a Mixed Infection of CBSV and UCBSV

Cassava brown streak disease (CBSD) caused by the Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) is a threat to cassava production in Africa. The potential spread of CBSD into West Africa is a cause for concern, therefore screening for resistance in farmer-preferred genotypes is crucial for effective control and management. We multiplied a selection of eleven cassava cultivars grown by farmers in Ghana to test their response to a mixed infection of CBSV (TAZ-DES-01) and UCBSV (TAZ-DES-02) isolates using a stringent top-cleft graft inoculation method. Virus titers were quantified in the inoculated scions and cuttings propagated from the inoculated scions to assess virus accumulation and recovery. All cultivars were susceptible to the mixed infection although their response and symptom development varied. In the propagated infected scions, CBSV accumulated at higher titers in leaves of eight of the eleven cultivars. Visual scoring of storage roots from six-month-old virus-inoculated plants revealed the absence of CBSD-associated necrosis symptoms and detectable titers of CBSVs in the cultivar, IFAD. Although all eleven cultivars supported the replication of CBSV and UCBSV in their leaves, the absence of virus replication and CBSD-associated symptoms in the roots of some cultivars could be used as criteria to rapidly advance durable CBSD tolerance using breeding and genetic engineering approaches.

Reaction of Cotton Genotypes to Meloidogyne Incognita Race 3 and Selection Ofisolates With High Reproductive Rate in Cotton

Background: Among the pathogens that reduce cotton productivity in Brazil, Meloidogyne incognita is one of the most important as it causes severe yield losses and is widespread. The most recommended methods for control of this species are the use of resistant cultivars and crop rotation systems. In Brazil, M. incognita races 3 and 4 have already been reported as cotton parasites but the race 3 is the most commonly found and widely disseminated.This work aimed at selecting virulent and aggressive populations of M. incognita race 3 for testing sources of resistance to this nematode in cotton genotypes.Results: The three isolates of M. incognita race 3 were important for screening of resistant cotton genotypes. The isolate from Umuarama was the most aggressive followed by Moreira Sales and Iporã. The genotypes CD 05-419, CD 05-945, CD 05-1087 and CD 05-1170 showed good performance against M. incognita race 3 in both greenhouse and field conditions.Conclusions: The cotton genotypes CD05-945, CD05-1170, CD05-1087 and CD05-419 will be selected for future work involving tests for resistance against other important cotton pathogens. Those genotypes can also be used as source of genes for resistance to nematodes in cotton breeding programs. The search for virulent and aggressive M. incognita isolates was very important when screening for resistance in cotton germplasm.

Screening for Resistance to Pythium Root Rot among Twenty-three Caladium Cultivars

Pythium root rot, caused by Pythium myriotylum (Ridings and Hartman, 1976), is a very damaging disease to caladium plants (Caladium x hortulanum). Use of disease-resistant cultivars has been an effective and economically viable strategy for integrated management of major diseases in numerous crops. This strategy could be used to control pythium root rot in caladium if resistant cultivars could be identified or developed. In an evaluation of 19 major commercial cultivars, 'Candidum', 'Candidum Jr.', 'Frieda Hemple', and 'White Christmas' were found to have a moderate level of resistance to Pythium. To find more resistant cultivars, twenty-three additional commercial cultivars were screened using the same Pythium isolates, inoculation and evaluation procedures as described earlier (Deng et al. 2004). This document is ENH1008, one of a series of the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date September 27, 2005. ENH1008/EP259: Screening for Resistance to Pythium Root Rot among Twenty-three Caladium Cultivars (ufl.edu)