Late Leaf Spot Research Articles

Screening of Groundnut (Arachis hypogaea L.) Genotypes for Identification of Sources of Resistance against Leaf Spot Disease

Background: Groundnut (Arachis hypogaea L.) is the fourth most important oil seed crop in the world. The early and late spots are a foliage disease more common and more destructive of groundnut which cause severe yield losses up to 70% and reduces the quality of the pod and fodder. Recent efforts have targeted on developing resistant source against leaf spot disease which are helpful for discarding the hazardous toxic chemical compounds used for controlling the disease. The current study aimed to identify the sources of resistance to leaf spot from the newly identified genotypes as well as from wild species and to study the way in which these were responding to the to the disease development. Methods: Seventy three groundnut genotypes were screened against late leaf spot disease under artificial epiphytotic conditions in field at AICRP on Groundnut, MPKV, Rahuri during kharif 2015-16. The observations of disease intensity and rate of infection were recorded. Result: Among the Seventy three groundnut genotypes, 10 genotypes showed resistant and 33 genotypes showed the moderately resistant reaction to leaf spot disease. The 25 entries showed the susceptible and 05 genotypes showed the highly susceptible reaction to the leaf spot disease. All the susceptible cultivars belong to A. hypogaea sub. sp. fastigiata var. fastigiata to as Spanish bunch. These 10 resistant genotypes of groundnut including two wild species viz., RHRG 6083, KDG 128, GPBD 4, ICGV 94118, ICGV 4983, ICG 12672, ICGV 13160 (A. batizocoi), ICGV 13165 (A. cardenasi), ICG 11426 and ICGV8193 were selected for intensive artificial screening under glasshouse conditions and also confirmed resistance. The resistant lines will be useful to develop introgression lines using marker-assisted backcrossing approach to improve foliar fungal disease resistance in popular groundnut varieties.

Sixty-One Years Following Registration, Phorate Applied In-Furrow at Planting Suppresses Development of Late Leaf Spot on Peanut.

Late and early leaf spot are caused by Nothopassalora personata and Passalora arachidicola, respectively, and are damaging diseases of peanut (Arachis hypogaea L.) capable of defoliation and yield loss. Management of these diseases is most effective through the integration of tactics that reduce starting inoculum and prevent infection. The insecticide phorate was first registered in 1959 and has been used in peanut production for decades in-furrow at planting to suppress thrips. Phorate further provides significant suppression of Tomato spotted wilt virus infection beyond suppression of its thrips vector alone by activating defense-related responses in the peanut plant. From six experiments conducted from 2017 to 2019 in Blackville, SC, Reddick, FL, and Quincy, FL, significantly less leaf spot defoliation was exhibited on peanuts treated with phorate in-furrow at planting (26%) compared with nontreated checks (48%). In-season fungicides were excluded from five of the experiments, whereas the 2018 Quincy, FL, experiment included eight applications on a 15-day interval. Across individual experiments, significant suppression of defoliation caused by late leaf spot was observed from 64 to 147 days after planting. Although more variable within location-years, pod yield following phorate treatment was overall significantly greater than for nontreated peanut (2,330 compared with 2,030 kg/ha; P = 0.0794). The consistent defoliation suppression potential was estimated to confer an average potential net economic yield savings of $90 to $120 per hectare under analogous leaf spot defoliation. To our knowledge, these are the first data in the 61 years since its registration demonstrating significant suppression of leaf spot on peanut following application of phorate in-furrow at planting. Results support phorate use in peanut as an effective and economical tactic to incorporate to manage late and early leaf spot infections and development of fungicide resistance.

Genetic diversity and population structure of groundnut (Arachis hypogaea L.) accessions using phenotypic traits and SSR markers: implications for rust resistance breeding

Groundnut (Arachis hypogaea L.) is a multi-purpose legume serving millions of farmers and their value chain actors globally. Use of old poor-performing cultivars contributes to low yields (< 1 t/ha) of groundnut in sub-Saharan Africa including Tanzania. The objectives of this study were to determine the extent of genetic variation among diverse groundnut collections using phenotypic traits and simple sequence repeat (SSR) markers to select distinct and complementary genotypes for breeding. One hundred and nineteen genotypes were evaluated under field conditions for agronomic traits and susceptibility to rust and leaf spot diseases. The study was conducted in two locations across two seasons. In addition, the 119 accessions were profiled with 13 selected SSR markers. Genotype and genotype by environment interaction effects were significant (p < 0.05) for days to flowering (DTF), late leaf spot score at 85 and 100 days after planting, pod yield (PDY), kernel yield (KY), hundred seed weight (HSW) and shelling percentage (SP). Principal components analysis revealed that plant stand, KY, SP, NPP (number of pods per plant), late leaf spot and rust disease scores accounted for the largest proportion of the total variation (71.9%) among the tested genotypes. Genotypes ICGV-SM 08587 and ICGV-SM 16579 had the most stable yields across the test environments. Moderate genetic variation was recorded with mean polymorphic information content of 0.34 and gene diversity of 0.63 using the SSR markers. The majority (74%) of genotypes showed high membership coefficients to their respective sub-populations, while 26% were admixtures after structure analysis. Much of the variation (69%) was found within populations due to genotypic differences. The present study identified genotypes ICGV-SM 06737, ICGV-SM 16575, ICG 12725 and ICGV-SM 16608 to be used for development of mapping population, which will be useful for groundnut improvement. This study provided a baseline information on characterization and selection of a large sample of groundnut genotypes in Tanzania for effective breeding and systematic conservation.

Fatty acid desaturase-2 (ahFAD2) mutant alleles in peanut (Arachis hypogaea L.) pre-breeding lines: an insight into the source, features, discourse, and selection of novel pre-breeding lines

High oleic peanuts and derived food products offer longer shelf life benefits to the food processing industry in addition to multiple health benefits to the consumers. The two mutant alleles, ahFAD2A and ahFAD2B control composition of oleic, linoleic and palmitic acid content in peanut. A total of 563 peanut pre-breeding lines were tested for the presence ahFAD2A and ahFAD2B mutant alleles using allele specific markers. The ahFAD2A mutant allele was present in 82 lines, while none of these lines had ahFAD2B mutant allele. Among botanical types, ahFAD2A mutant allele was more frequent in lines with Virginia growth habit than Spanish bunch although no correlation of ahFAD2A mutant allele with high oleic acid content and growth habit could be established. Oleic and linoleic acid content in 82 pre-breeding lines ranged from 39.70 to 62.70% and 17.76 to 31.95%, respectively, with maximum oleic to linoleic acid ratio of 4. Oleic acid was found to be negatively correlated with linoleic and palmitic acid. Further, pre-breeding lines with ahFAD2A mutant allele, high oleic content and high oleic to linoleic ratio were investigated and novel lines were identified for resistance to late leaf spot, short duration, higher pod yield and other yield related traits. These novel pre-breeding lines can be used as a potential donor in peanut improvement programme and to diversify the primary gene pool including initiating further research on induction of fresh ahFAD2B mutant allele.

Weather factor and chemical management against late leaf spot (LLB) and rust diseases under rainfed groundnut conditions

Groundnut (Arachis hypogaea L.) is most growing under rainfed conditions, the important disease of late leaf spot and rust reduction of yield in rainfed condition. Experiments were conducted 2012, 2013 and 2014. The temperature for three years minimum temperature 23.57 °C temperature 37.54 °C combination of weather conditions during the growing season of groundnut foliar diseases of Late leaf spot and Rust diseases for favourable severe conditions. Among the different chemicals tested for three years the combination of Carbendazim + Mancozeb (SAAF)@1.25Kg/ha recorded the least diseases incidence of Late leaf spot (22.36%) and rust (17.58%) with accounting of diseases reduction for late leaf spot (61.24%) and rust (70.03%) followed by carbendazim and chlorothlonil. The individual application copper hydroxide controlled the rust disease effectively when compared to other treatments also increased yield 1003.67kg/ha. The Carbendazim + Mancozeb (SAAF) @ 1.25kg/ha broad spectrum fungicide for reduced the spraying schedule and no of chemicals used and also protective and curative action with contact and systemic in nature groundnut cultivations under rain fed condition.

Effect of DMI and QoI fungicides mixed with the SDHI fungicide penthiopyrad on late leaf spot of peanut

In recent years, succinate dehydrogenase inhibiting (SDHI) fungicides have become important for control of early leaf spot (Passalora arachidicola) and late leaf spot (Nothopassalora personata) of peanut (Arachis hypogaea) in the southeastern U.S. In this study, pyraclostrobin, cyproconazole, and thiophanate-methyl were compared for efficacy alone and as mixing partners with SDHI fungicide penthiopyrad for control of late leaf spot. In all trials, mixtures of penthiopyrad + pyraclostrobin or penthiopyrad + cyproconazole improved leaf spot control compared to penthiopyrad alone based final percent defoliation, and in most cases based on area under the defoliation progress curve. Additional control provided by mixtures with thiophanate-methyl was minimal compared to penthiopyrad alone. In trials at Tifton and Plains, GA, efficacies of the mixtures of penthiopyrad + cyproconazole and penthiopyrad + pyraclostrobin were greater than expected based on performance of the respective individual fungicides, indicating synergistic effects of these fungicide combinations.

Molecular and phenotypic diversity of groundnut (Arachis hypogaea L.) cultivars in Togo.

Diversity assessment of 94 groundnut accessions from Togo and Senegal, using agro-morphological and SNP markers, revealed high variability for many quantitative traits such as late leaf spot (LLS) incidence, number of pods per plant and yield per plant. For qualitative traits, the Simpson Index showed high diversity for primary seed colour (0.75), stem pigmentation (0.60), and Growth habit (0.59). Principal component analysis underscored quantitative traits such as hundred seed weight, days to maturity, and LLS incidence, as the main traits contributing to the divergence. Correlation and path coefficient analysis showed that the number of pods per plant was the main yield-related trait positively affecting yield (r = 0.95, PC = 0.84; p = 0.01). Overall, 990 SNP markers revealed moderate genetic variability in the genotypes and the percentage of heterozygous genotypes varied from 0 to 50% for all loci. Analysis of molecular variance revealed that only 1.1% of the total molecular variance accounted for geographical contribution to the diversity. Co-analysis of phenotypic and SNP data delineated three clusters harbouring useful alleles and interesting phenotypic features such as LLS resistance, large number of pods per plant and early maturity indicating that differences observed at the phenotypic level are underlined by genotypic differences. The phenotypic and genotypic diversity observed could be exploited for the identification of parents with preferred traits for use in the breeding program. However, the low population structure highlights the necessity to improve groundnut diversity in Togo through introduction from various sources.

Combining High Oleic Acid Trait and Resistance to Late Leaf Spot and Rust Diseases in Groundnut (Arachis hypogaea L.)

High oleic trait, resistance to rust and late leaf spot (LLS) are important breeding objectives in groundnut. Rust and LLS cause significant economic loss, and high oleic trait is an industry preferred trait that enhances economic returns. This study reports marker-assisted selection to introgress high oleic content, resistance to LLS and rust into Kadiri 6 (K 6), a popular cultivar. The alleles for target traits were selected using linked allele-specific, simple sequence repeats and single nucleotide polymorphic markers. The F1s (384), intercrossed F1s (441), BC1F1s (380), BC1F2s (195), and BC1F3s (343) were genotyped to obtain desired allelic combination. Sixteen plants were identified with homozygous high oleic, LLS and rust resistance alleles in BC1F2, which were advanced to BC1F3 and evaluated for disease resistance, yield governing and nutritional quality traits. Phenotyping with Near-Infrared Reflectance Spectroscopy identified three lines (BC1F3-76, BC1F3-278, and BC1F3-296) with >80% oleic acid. The identified lines exhibit high levels of resistance to LLS and rust diseases (score of 3.0–4.0) with preferred pod and kernel features. The selected lines are under yield testing trials in multi-locations for release and commercialization. The lines reported here demonstrated combining high oleic trait with resistance to LLS and rust diseases.

Marker assisted introgression of QTL region to improve late leaf spot and rust resistance in elite and popular variety of groundnut (Arachis hypogaea L.) cv TMV 2

Late leaf spot (LLS) and rust diseases are the major devastating diseases in groundnut that lowers crop yield and fodder quality. Marker assisted backcross breeding was employed to introgress LLS and rust diseases resistance QTL region from GPBD 4 into an India’s popular groundnut variety TMV 2. The MABC approach was exercised using a total of eight disease resistance-linked markers viz.., IPAHM103, GM1573, GM1009, Seq8D09, GM2009, GM1536, GM2301 and GM2079 present in the QTL region. After three backcrosses and selfing, a total of 155 BC3F2 lines were developed from the cross TMV 2 x GPBD 4. Ten BC3F2 homozygous introgression lines were identified with resistance QTL region and subjected to background analysis. A genome recovery upto 99.80% was observed among introgression lines and advanced to further generations for field evaluation. Finally, six ILs with enhanced late leaf spot and rust diseases resistance were identified. Those ILs had significantly increased pod yield (42–65%) over the recurrent parent TMV 2 with enhanced resistance to LLS and rust diseases. Multi-location field evaluation of these ILs could leads to the release of improved varieties and also can be used as genetic resources in the groundnut improvement.

G × E interactions in QTL introgression lines of Spanish-type groundnut (Arachis hypogaea L.)

Multi-environment testing at five locations for rust and late leaf spot (LLS) resistance with 41 introgressed lines (ILs) bred using marker-assisted backcross breeding in the genetic background Spanish-type groundnut varieties identified significant genotype, and genotype × environment interactions (GEI) for LLS disease resistance and yield parameters. Significant GEI effects suggest the need to identify location specific breeding lines to achieve gains in pod yield and LLS resistance. The observed variable LLS disease reaction among the ILs in part suggests influence of background genotype on the level of resistance. A breeding scheme with early generation selection using molecular markers followed by phenotyping for LLS, and multi-location testing of fixed breeding lines was optimized to enhance selection intensity and accuracy in groundnut breeding. The ILs, ICGVs 14431, 14436 and 14438 with pooled LLS score at 90 DAS of 3.5–3.7 were superior to respective recurrent parent for pod yield, with early maturing similar to recurrent parents. The pod yield advantage in ILs is attributed by more number of pods, besides resistance to LLS that contributes to better filling.

Automatic method for classification of groundnut diseases using deep convolutional neural network

Groundnut is one of the most important and popular oilseed foods in the agricultural field, and its botanical name is Arachis hypogaea L. Approximately, the pod of mature groundnut contains 1–5 seeds with 57% of oil and 25% of protein content. The oil obtained from the groundnut is widely used for cooking and losing body weight, and its fats are widely used for making soaps. The groundnut cultivation is affected by different kinds of diseases such as fungi, viruses, and bacteria. Hence, these diseases affect the leaf, root and stem of the groundnut plant and it leads to heavy loss in yield. Moreover, the enlarger number of diseases affects the leaf and root-like Alternaria, Pestalotiopsis, Bud necrosis, tikka, Phyllosticta, Rust, Pepper spot, Choanephora, early and late leaf spot. To overcome these issues, we introduce an efficient method of deep convolutional neural network (DCNN) because it automatically detects the important features without any human supervision. The DCNN procedure can deeply detect plant disease by using a deep learning process. Moreover, the DCNN training and testing process demonstrate an accurate groundnut disease determination and classification result. The number of groundnut leaf disease images is chosen from the plant village dataset, and it is used for the training and testing process. The stochastic gradient decent momentum method is used for dataset training, and it has shown the better performance of proposed DCNN. From the comparison analysis, the 6th combined layer of proposed DCNN delivers a 95.28% accuracy value. Ultimately, the groundnut disease classification with its overall performance of proposed DCNN provides 99.88% accuracy.

Peanut Yield Loss in the Presence of Defoliation Caused by Late or Early Leaf Spot.

Late and early leaf spot, respectively caused by Nothopassalora personata and Passalora arachidicola, are damaging diseases of peanut (Arachis hypogaea) capable of defoliating canopies and reducing yield. Although one of these diseases may be more predominant in a given area, both are important on a global scale. To assist informed management decisions and quantify relationships between end-of-season defoliation and yield loss, meta-analyses were conducted over 140 datasets meeting established criteria. Slopes of proportion yield loss with increasing defoliation were estimated separately for Virginia and runner market type cultivars. Yield loss for Virginia types was described by an exponential function over the range of defoliation levels, with a loss increase of 1.2 to 2.2% relative to current loss levels per additional percent defoliation. Results for runner market type cultivars showed yield loss to linearly increase 2.2 to 2.8% per 10% increase in defoliation for levels up to approximately 95% defoliation, after which the rate of yield loss was exponential. Defoliation thresholds to prevent economic yield loss for Virginia and runner types were estimated at 40 and 50%, respectively. Although numerous factors remain important in mitigating overall yield losses, the integration of these findings should aid recommendations about digging under varying defoliation intensities and peanut maturities to assist in minimizing yield losses.

Association of late leaf spot (LLS) and rust resistance with yield in selected peanut genotypes

In this study, seventy five peanut genotypes of groundnut were analyzed for association between diseaseresistance and kernel yield in kharif under two locations (Coimbatore and Aliyar Nagar). The result indicated nonsignificant association between the disease severity and yield.

Identification of QTLs for resistance to leaf spots in cultivated peanut (Arachis hypogaea L.) through GWAS analysis.

Two QTLs on ChrB09 significantly associated with both early and late leaf spots were identified by genome-wide association study in the US peanut mini-core collection. Early leaf spot (ELS) and late leaf spot (LLS) are two serious peanut diseases in the USA, causing tens of millions of dollars of annual economic losses. However, the genetic factors underlying resistance to those diseases in peanuts have not been well-studied. We conducted a genome-wide association study for the two peanut diseases using Affymetrix version 2.0 SNP array with 120 genotypes mainly coming from the US peanut mini-core collection. A total of 46 quantitative trait loci (QTLs) were identified with phenotypic variation explained (PVE) from 10.19 to 24.11%, in which eighteen QTLs are for resistance to ELS and 28 QTLs for LLS. Among the 46 QTLs, there were four and two major QTLs with PVE higher than 16.99% for resistance ELS and LLS, respectively. Of the six major QTLs, five were located on the B sub-genome and only one was on the A sub-genome, which suggested that the B sub-genome has more potential resistance genomic regions than the A sub-genome. In addition, two genomic regions on chromosome B09 were found to provide significant resistance to both ELS and LLS. A total of 74 non-redundant genes were identified as resistance genes, among which, twelve candidate genes were in significant genomic regions including two candidate genes for both ELS and LLS, and other ten candidate genes for ELS. The QTLs and candidate genes obtained from this study will be useful to breed peanuts for resistances to the diseases.

Improved Management Efficacy of Late Leaf Spot on Peanut Through Combined Application of Prothioconazole with Fluxapyroxad and Pyraclostrobin

Late leaf spot, caused by Nothopassalora personata, is the most economically important fungal disease affecting peanut foliage in South Carolina and can result in combined management and yield loss costs of greater than 490 dollars/ha. Application of protectant fungicides is a critical part of effective integrated management under commercial production, and their strategic alternation and combination in management programs can provide enhanced control. Trials were conducted in Blackville, SC, from 2017 to 2019 to investigate whether combinations of prothioconazole with fluxapyroxad plus pyraclostrobin could provide more efficacious management of late leaf spot compared to either product alone. Two applications of 0.11 kg/ha prothioconazole with 0.05 kg/ha fluxapyroxad plus 0.1 kg/ha pyraclostrobin resulted in significantly (p &lt; 0.05) less (24% to 42%) peanut canopy defoliation compared to the same number of applications of either product applied individually, with the combined application reflecting significant (p &lt; 0.0202) synergism compared to component products as assessed through independent action methodology. An increased rate of fluxapyroxad plus pyraclostrobin application (0.1 and 0.2 kg/ha, respectively), with 0.16 kg/ha prothioconazole did not improve management relative to their combination at the examined lower rate (p = 0.89). Peanut yield was not adversely affected following combined applications. Cost-effectiveness of this combination depends on the actual disease intensity and yield potential of a given crop.

Evaluation of Improved Valencia Peanut Varieties for Production in Haiti

ABSTRACT Late leaf spot (Cercosporidium personatum) and peanut rust (Puccinia arachidis) are the most important diseases of peanut (Arachis hypogaea L.) in Haiti. Traditional Haitian peanut varieties are not only susceptible to these diseases but are also typically grown without benefit of a fungicide program. Five trials were conducted from 2015 to 2017 to evaluate the performance of six Valencia varieties in Quartier-Morin, Haiti (with an additional trial in 2017 at the Central Plateau) with respect to yield, resistance to rust and leaf spot diseases, and response to a fungicide program. A split-plot design with four or six replications was used in these studies. In each, “variety” was the whole plot and presence or absence of a fungicide program was the subplot. Valencia market types 309 Red, 309 Tan, M2, M3, SGV0801 and a local landrace were compared with and without Muscle ADV (tebuconazole + chlorothalonil, Sipcam) (2.3 L/ha) applied at 45, 60 and 75 days after planting (DAP). Final disease ratings (late leaf spot and peanut rust) were assessed approximately 94 DAP and plots were harvested the day following. In all trials, 309 Tan variety had the least amount of leaf spot and rust, but resulted in the lowest yield in four out of five trials, averaging 1727 kg/ha across fungicide treatments. M3, M2 and 309 Red were generally the numerically highest-yielding varieties, averaging 2906, 2864 and 2541 kg/ha across fungicide treatments, respectively, but were not statistically higher than the local Haitian Valencia, averaging 2374 kg/ha. Three fungicide applications during the season significantly increased yields in most trials for all varieties except 309 Tan. The highest and lowest average increase in yield from fungicide was for 309 Red (1126 kg/ha) and 309 Tan (103 kg/ha), respectively. The results from this study conducted over 2 years and 4 seasons document that while resistance to late leaf spot and rust is available in Valencia varieties, yield potential is not directly associated with that resistance. Also, use of fungicide improves yield potential in more susceptible varieties.

Rapid Detection of Fungicide Resistance Phenotypes Among Populations of Nothopassalora personata in South Carolina Peanut Fields

We evaluated the occurrence of fungicide resistance phenotypes in populations of Nothopassalora personata, the causal agent of late leaf spot (LLS), sampled from South Carolina peanut fields in 2018 using a modified detached leaf assay (DLA). Spore suspensions obtained from each of 72 groups of LLS-symptomatic leaves collected from nine counties were used in the DLA to examine phenotypic resistance to four site-specific fungicides (azoxystrobin, benzovindiflupyr, prothioconazole, and thiophanate-methyl) and one multisite contact fungicide (chlorothalonil). Lesion development was measured as a binary event in which presence of a lesion indicated control failure (phenotypic resistance) and absence of a lesion indicated successful control (sensitivity). Phenotypic resistance probabilities of N. personata samples to each site-specific fungicide were compared against the control fungicide (chlorothalonil). Variation in phenotypic resistance probabilities to the four single-site fungicides was observed from most counties (6 of 9), with frequencies of phenotypic resistance having differed among counties. The DLA facilitated rapid evaluation of N. personata phenotypic resistance to azoxystrobin, benzovindiflupyr, prothioconazole, and thiophanate-methyl. This assay has potential to be used as an alternative method for routine monitoring of phenotypic resistance, identification of populations to test for the presence of resistance genes, and improving reliability of current fungicide recommendations.

Utilization of Advanced Backcross Population Derived from Synthetic Amphidiploid for Dissecting Resistance to Late Leaf Spot in Peanut (Arachis hypogaea L.)

Late leaf spot (LLS) is the major foliar disease, which often occur with rust and cause severe yield losses worldwide in peanut (Arachis hypogaea L.). In order to map and introgress the resistance alleles for LLS into an elite cultivar ICGS 76, the advanced backcross approach was used for identification of quantitative trait locus (QTL). The synthetic amphidiploid ISATGR 278–18 (A. duranensis ICG 8138 × A. batizocoi ICG 13160) which is known to harbor resistance alleles for foliar diseases was used as donor parent to generate AB-QTL population comprising of 164 introgression lines (ILs). A linkage map with 114 microsatellite markers was developed spanning 746.15 cM distance with an average inter-marker distance of 6.55 cM. QTL analysis yielded 14 main-effect QTLs (mQTLs) (explaining up to 38.58% PVE) for LLS and 10 mQTLs (up to 10.99% PVE) for rust. In addition, four epistatic QTLs (eQTLs) (explaining up to 4.97% PVE) were observed for foliar diseases. Furthermore, seven mQTLs and 16 eQTLs were observed for agronomic traits. Several ILs showed high resistance to LLS with agronomic attributes from recurrent parent. This study reports the utilization of the untapped resistance source for LLS from A. batizocoi that was not extensively used earlier in peanut crop improvement.

Major seed size QTL on chromosome A05 of peanut (Arachis hypogaea) is conserved in the US mini core germplasm collection

Pod and seed size are important characteristics for the peanut industry and have been under strong selection pressure since peanut domestication. In order to dissect the genetic control of peanut pod and seed size, a recombinant inbred mapping population from a cross of Florida-07 by GP-NC WS 16 was used to determine the genomic regions associated with traits including 100 pod weight, 100 seed weight, pod weight of double-seeded pods, seed weight of double-seeded pods, and area of double-seeded pods. Nine QTL on linkage groups (LGs) A05, A06, A09, B10, B04, A03, B05, and B08 were associated with pod and seed size. A majority of the QTL have small effects except the locus on LG A05 (93 to 102 Mbp) which explained up to 66% phenotypic variation for all measured pod and seed traits. A comparison of QTL previously reported for yield component traits showed a common QTL on LG A05 was detected in two genetic populations whose parentage is distinct from those used in this study. The markers tightly linked to this major QTL were informative in distinguishing large versus small-seeded germplasm lines in the mini core collection originating from thirty-one countries, suggesting selection for this seed size QTL in large-seeded ecotypes. However, the large seed size allele appeared to co-segregate with a late leaf spot disease susceptibility allele inherited from the Florida-07 parent. Therefore, peanut breeders need to weigh the pros and cons before integrating the large seed size QTL from Florida-07 in their breeding program.

Steady expression of high oleic acid in peanut bred by marker-assisted backcrossing for fatty acid desaturase mutant alleles and its effect on seed germination along with other seedling traits.

Peanut (Arachis hypogaea L.) is an important nutrient-rich food legume and valued for its good quality cooking oil. The fatty acid content is the major determinant of the quality of the edible oil. The oils containing higher monounsaturated fatty acid are preferred for improved shelf life and potential health benefits. Therefore, a high oleic/linoleic fatty acid ratio is the target trait in an advanced breeding program. The two mutant alleles, ahFAD2A (on linkage group a09) and ahFAD2B (on linkage group b09) control fatty acid composition for higher oleic/linoleic ratio in peanut. In the present study, marker-assisted backcrossing was employed for the introgression of two FAD2 mutant alleles from SunOleic95R into the chromosome of ICGV06100, a high oil content peanut breeding line. In the marker-assisted backcrossing-introgression lines, a 97% increase in oleic acid, and a 92% reduction in linoleic acid content was observed in comparison to the recurrent parent. Besides, the oleic/linoleic ratio was increased to 25 with respect to the recurrent parent, which was only 1.2. The most significant outcome was the stable expression of oil-content, oleic acid, linoleic acid, and palmitic acid in the marker-assisted backcrossing-introgression lines over the locations. No significant difference was observed between high oleic and normal oleic in peanuts for seedling traits except germination percentage. In addition, marker-assisted backcrossing-introgression lines exhibited higher yield and resistance to foliar fungal diseases, i.e., late leaf spot and rust.