Incidence of Root-Knot Nematode (Meloidogyne graminicola) and Resulting Crop Losses in Paddy Rice in Northern India

Surveys of major rice growing districts in the state of Uttar Pradesh in Northern India were conducted for 3 consecutive years during 2013 to 2015 under a government-funded major research project to determine the frequency of occurrence and disease incidence of the rice root-knot nematode, Meloidogyne graminicola, in rice paddy fields. More than 800 paddy fields from 88 Tehsils (divisions within a district) in 18 major rice growing districts in Uttar Pradesh were surveyed, where M. graminicola was associated with root-knot disease in rice paddy fields based on morphological and molecular characterization of juveniles and adults. The highest frequency of disease in rice fields was observed in Aligarh (44.6%), followed by Muzaffarnagar, Shahjahanpur, and Kheri Lakhimpur (29.3, 28.0, and 27.4%, respectively). Maximum disease incidence was also recorded in Aligarh (44.6%), followed by Sultanpur, Mainpuri, and Muzaffarnagar (5.7, 5.2, and 4.5, respectively). Gall index and egg mass index values (on a 0 to 10 scale) were highest in Aligarh (3.5 and 2.1, respectively), followed by Muzaffarnagar (2.6 and 2.0) and Mainpuri (2.3 and 1.8). The average soil population of M. graminicola was highest in Aligarh (3,851 ± 297 second-stage juveniles [J2]/kg of soil), followed by Muzaffarnagar (2,855 ± 602 J2/kg of soil), whereas the lowest population was recorded in Barabanki (695 ± 400 J2/kg of soil) at the time of harvesting. Relative yield losses were also determined, and the highest yield loss attributed to M. graminicola infestation was recorded in Aligarh (47%). The yield loss was linearly correlated with the soil population density of M. graminicola and disease incidence.

Potential of non-fumigant nematicides at different formulations against southern root-knot nematode (Meloidogyne incognita) on tomato plants

Currently, plant parasitic nematodes (PPN) especially root knot nematodes, Meloidogyne spp. have been found involved in the global losses of tomato crops. The most employed tactic for managing PPN in Africa is non-fumigant nematicides. Recently, in Egypt abamectin was recorded as a new tool to control PPN. Thus, two pot experiments were conducted to evaluate the potential of abamectin and certain non-fumigant nematicides namely; oxamyl and ethoprophos at two different formulations (granular and liquid) against southern root knot nematode (Meloidogyne incognita) on tomato plants under greenhouse conditions. Results revealed the granular formulations of ethoprophos and oxamyl, in addition to abamectin, showed the same significance (P≤0.05) in suppressing tomato soil population and root galls of M. incognita, during both experiments. However, liquid formulations of ethoprophos and oxamyl gave relatively less decreasing in soil population and root galls. On the other hand, all applied treatments improved plant growth criteria ranging from 36.92 to 126.44% in shoot dry weight and from 31.25 to 137.50% in root dry weight for both experiments.

Population Genomics Analysis of Legume Host Preference for Specific Rhizobial Genotypes in the Rhizobium leguminosarum bv. viciae Symbioses

Rhizobium leguminosarum bv. viciae establishes root nodule symbioses with several legume genera. Although most isolates are equally effective in establishing symbioses with all host genera, previous evidence suggests that hosts select specific rhizobial genotypes among those present in the soil. We have used population genomics to further investigate this observation. Pisum sativum, Lens culinaris, Vicia sativa, and V. faba plants were used to trap rhizobia from a well-characterized soil, and pooled genomic DNA from 100 isolates from each plant were sequenced. Sequence reads were aligned to the R. leguminosarum bv. viciae 3841 reference genome. High overall conservation of sequences was observed in all subpopulations, although several multigenic regions were absent from the soil population. A large fraction (16 to 22%) of sequence reads could not be recruited to the reference genome, suggesting that they represent sequences specific to that particular soil population. Although highly conserved, the 16S to 23S ribosomal RNA gene region presented single nucleotide polymorphisms (SNP) regarding the reference genome, but no striking differences could be found among plant-selected subpopulations. Plant-specific SNP patterns were, however, clearly observed within the nod gene cluster, supporting the existence of a plant preference for specific rhizobial genotypes. This was also shown after genome-wide analysis of SNP patterns.

Effect of Cultivar Selection on Soil Population of Verticillium dahliae and Wilt Development in Cotton

A microplot study was conducted over a 3-year period to investigate the influence of planting combinations of susceptible and/or partially resistant cotton cultivars on soil population of Verticillium dahliae. Stoneville (ST) 4554B2RF was used throughout the test as a susceptible cultivar and either Associated Farming Delinting (AFD) 5065B2F or an advanced breeding line was used as a partially resistant cultivar. Microplots were augmented with field soil naturally infested with V. dahliae. ST 4554B2RF when planted in three sequential seasons increased V. dahliae population in soil by 754 fold; however, V. dahliae population in microplots planted to the partially resistant cultivars over three seasons increased by 114 fold. Disease incidence increased from 8% to 58% over 3 years for ST 4554B2RF and from 0% to 5% for AFD 5065B2F or advanced breeding line over the same period. Yield was highest after 3 years of AFD 5065B2F or the advanced breeding line and lowest after 3 years of ST 4554B2RF. Yield correlated with the current year cultivar, pre-plant V. dahliae densities, and disease incidence. Results from this study indicate that cultivar selection can impact microsclerotia density and incidence of wilt in cotton. Accepted for publication 26 June 2012. Published 24 August 2012.

Coniothyrium minitans survival in soil and ability to infect sclerotia of Sclerotinia sclerotiorum

Survival of the sclerotial parasite Coniothyrium minitans in soil when applied as spore suspension or colonised solid substrate (maizemealperlite) inocula and ability to infect Sclerotinia sclerotiorum sclerotia incorporated into the soil after different times was assessed over 6 months Unambiguous detection of the C minitans isolate from the indigenous C minitans soil population was achieved using a hygromycin B resistant transformant (T3) which was similar in behaviour to the wild type LU112 Coniothyrium minitans was recovered from soil by dilution plating at all assessment times with higher recovery from spore suspension compared with maizemealperlite amended soil Coniothyrium minitans was able to infect and reduce viability of sclerotia incorporated into the amended soil over the 6 month experiment with spore suspension significantly increasing infection compared with maizemealperlite inoculum Hygromycin B amendment of the agar significantly increased C minitans recovery from sclerotia especially when the population of secondary fungal colonisers was high

Relationship between Alternaria radicina soil population density and carrot black rot

Alternaria radicina is a seed and soilborne pathogen that causes black rot of carrot tap roots and black rings on the root crown The A radicina population density in spring was determined in carrot field soils to investigate the relationship between soil conidial populations and black rot levels in summer In each of 15 carrot fields four randomly selected 30 m2 plots were used for soil sampling to a depth of 5 cm in September Alternaria radicina population densities (cfu/g soil) were determined using a soil dilution method and selective agar Black rot disease incidence was expressed as the number of infected plants/m of row and severity was assessed using a 0 to 4 rating scale Alternaria radicina soil population density (33233 cfu/g soil) correlated positively (P

Genetic characterization and nitrogen fixation capacity of Rhizobium strains on common bean

This study aimed to genetically characterize four new Rhizobium strains, and to evaluate their nodulation and fixation capacity compared to commercial strains and to native rhizobia population of a Brazilian Rhodic Hapludox. Two experiments were carried out in randomized blocks design, under greenhouse conditions, in 2007. In the first experiment, the nodulation and nitrogen fixation capacity of new strains were evaluated, in comparison to the commercial strains CIAT-899 and PRF-81 and to native soil population. It was carried out in plastic tubes filled with vermiculite. DNA extractions and PCR sequencing of the intergenic space were made from the isolated pure colonies, in order to genetically characterize the strains and the native rhizobia population. In the second experiment, the nodulation and productivity of common beans Perola cultivar were determined, with the use of evaluated strains, alone or in mixture with PRF-81 strain. It was carried out in pots filled with soil. The native soil population was identified as Rhizobium sp. and was inefficient in nitrogen fixation. Three different Rhizobium species were found among the four new strains. The LBMP-4BR and LBMP-12BR new strains are among the ones with greatest nodulation and fixation capacity and exhibit differential responses when mixed to PRF-81.