Martin John Wubben

Three upland cotton ( Gossypium hirsutum L.) germplasm lines, USDA‐ARS‐GNLO1 (Reg. no. GP‐1171, PI 708333), USDA‐ARS‐GNLO2 (Reg. no. GP‐1172, PI 708334), and USDA‐ARS‐GNLO3 (Reg. no. GP‐1173 PI 708335), containing high seed oil oleic acid and increased resistance to root‐knot and reniform plant‐parasitic nematodes were developed and released by the USDA‐ARS. The stability of the high‐oleic acid oil trait was evaluated by examining its effects on plant agronomic performance and seed traits across multiple generations and geographic locations. This trait was originally identified in G. barbadense L. accession GB713 (PI 608139) and bred into the upland cotton cultivar Sure‐Grow 747 (SG747, PVP 9800118) as part of a nematode resistance breeding program. Starting with the previously analyzed F ₅ seed, plants producing high oleic acid were selected based on seed oil fatty acid distribution analyses. Plants producing >50% seed oleic acid were analyzed for seed oil content, protein and gossypol levels, fiber properties, and warm germination competency. The three lines consistently produced seed oleate levels >50%, which is triple the 15%–19% observed in standard cottonseed oil and higher than the 33%–35% levels found in previously released ‘HOa’ lines (HOa1–HOa4). Oleate levels in the USDA‐ARS‐GNLO lines surpassed those of the original G. barbadense GB713 parent, suggesting synergistic effects between gene alleles from the G. hirsutum and G. barbadense parental genotypes in the new germplasm lines. Oil with this composition should demonstrate competitive deep‐fat‐frying properties and help extend the shelf life of other food products, such as spreads and salad dressings.

The reniform nematode (Rotylenchulus reniformis Linford & Oliveira) is a serious pathogen of Upland cotton (Gossypium hirsutum L.) wherever it is grown throughout the United States. Upland cotton resistance to R. reniformis derived from the G. barbadense accession GB713 is largely controlled by the Ren^barb2 locus on chromosome 21. Ren^barb2 has proven useful as a tool to mitigate annual cotton yield losses due to R. reniformis infection; however, very little is known about the molecular aspects of Ren^barb2-mediated resistance and the gene expression changes that occur in resistant plants during the course of R. reniformis infection. In this study, two nearly isogenic lines (NILs), with and without the Ren^barb2 locus, were inoculated with R. reniformis and RNAs extracted and sequenced from infected and control roots at 5-, 9-, and 13-dai (days after inoculation). A total of 966 differentially expressed genes (DEGs) were identified in the resistant NIL while 133 DEGs were discovered from the susceptible NIL. In resistant plants, biological processes related to oxidation-reduction reactions and redox homeostasis were enriched at each timepoint with such genes being up-regulated at 5- and 9-dai but then being down-regulated at 13-dai. DEGs associated with cell wall reinforcement and defense responses were also up-regulated at early timepoints in resistant roots. In contrast, in susceptible roots, defense-related gene induction was only present at 5-dai and was comprised of far fewer genes than in the resistant line. ERF, WRKY, and NAC transcription factor DEGs were greatly enriched at 13-dai in resistant roots but were absent in the susceptible. Cluster analysis of resistant and susceptible DEGs revealed an ‘early’ and ‘late’ response in resistant roots that was not present in the susceptible NIL. SNP analysis of transcripts within the Ren^barb2 QTL interval identified five genes having non-synonymous mutations shared by other Ren^barb2 germplasm lines. The basal expression of a single candidate gene, Gohir.D11G302300, a CC-NBS-LRR homolog, was ~3.5-fold greater in resistant roots versus susceptible. These data help us to understand the Ren^barb2-mediated resistance response and provides a short list of candidate resistance genes that potentially mediate that resistance.

The root‐knot nematode (RKN; Meloidogyne incognita Kofoid & White) and reniform nematode (RN; Rotylenchulus reniformis Linford & Oliveira) are serious pathogens of upland cotton (Gossypium hirsutum L.) that significantly affect yield and fiber quality annually. Here, we describe two upland cotton germplasm lines that have combined resistance to RKN and RN while maintaining good yield and fiber quality traits. Upland germplasm lines MS‐4857 (Reg. no. GP‐1147, PI 704481) and MS‐4878 (Reg. no. GP‐1148, PI 704482) are F₆ recombinant inbred lines from a cross between M240 RNR (RKN resistant) and MT2468 Ren1 (moderately RN resistant). These lines are highly resistant to RKN and show ∼30% fewer RN eggs g⁻¹ root than the MT2468 Ren1 parent due to significantly improved root system development compared with MT2468 Ren1. Yield and fiber quality traits are equivalent or superior to the parental lines. The upland‐derived RN resistance in these lines provides a valuable alternative source of resistance to cotton breeding programs, especially in combination with high‐level RKN resistance.

Meloidogyne enterolobii [the guava root-knot nematode (RKN)] is an emerging plant-parasitic nematode that poses a threat to Upland cotton ( Gossypium hirsutum ) production in the southeastern United States. Like other RKN spp., M. enterolobii has a wide host range and proven ability to overcome resistance sources that have helped protect crops from other Meloidogyne spp., including the southern RKN ( Meloidogyne incognita ). In this study we evaluated the virulence of two North Carolina M. enterolobii isolates on Upland cotton germplasm lines having resistance quantitative trait loci (QTL) to RKN (M240 RNR, MRk-Rn-1) and/or reniform nematode ( Rotylenchulus reniformis ) (M713 Ren1, MRk-Rn-1) in comparison to their susceptible recurrent parents (DPL61, SG747). Multiple assays using eggs or J2 as inoculum demonstrated that both isolates reproduced equally well on all germplasm lines, producing reproductive factor (RF) values ≥ 6 on the otherwise nematode-resistant lines. Measurements of seedling growth in control and inoculated containers suggested that existing nematode-resistance QTL may offer a level of tolerance to M. enterolobii infection that should be further explored in greenhouse and field environments. Meloidogyne enterolobii infection of SG747 and MRk-Rn-1 showed nearly identical stages of symptom and nematode development over a time-course of 24 days. These data demonstrate that existing RKN and RN resistance QTL available in elite cotton varieties to producers are most likely insufficient in preventing yield loss due to M. enterolobii and that future research should focus on (i) understanding the M. enterolobii –cotton interaction at the molecular level, and (ii) screening novel germplasm collections to identify resistance loci.

Upland cotton encounters biotic and abiotic stresses during the growing season, which significantly affects the genetic potential of stress tolerance and productivity. The root-knot nematode (RKN) (Meloidogyne incognita) is a soilborne roundworm affecting cotton production. The occurrence of abiotic stress (drought stress, DS) can alter the plant–disease (RKN) interactions by enhancing host plant sensitivity. Experiments were conducted for two years under greenhouse conditions to investigate the effect of RKN and DS and their combination using nematode-resistant (Rk-Rn-1) and nematode susceptible (M8) cotton genotypes. These genotypes were subjected to four treatments: control (100% irrigation with no nematodes), RKN (100% irrigation with nematodes), DS (50% irrigation with no nematodes), and DS + RKN (50% irrigation with nematodes). We measured treatments-induced changes in cotton (i) leaf reflectance between 350 and 2500 nm; and (ii) physiology and biomass-related traits for diagnosing plant health under combined biotic and abiotic stresses. We used a maximum likelihood classification model of hyperspectral data with different dimensionality reduction techniques to learn RKN and DS stressors on two cotton genotypes. The results indicate (i) the RKN stress can be detected at an early stage of 10 days after infestation; (ii) RKN, DS, and DS + RKN can be detected with an accuracy of over 98% using bands from 350–1000 nm and 350–2500 nm. The genotypes ‘Rk-Rn-1’and ‘M8’ showed differential responses to DS, RKN, and DS + RKN. With a few exceptions, all three stressors reduced the pigments, physiology, and biomass traits and the magnitude of reduction was higher in ‘M8’ than ‘Rk-Rn-1’. Observed impact of stressors on plant growth followed DS + RKN > DS > RKN. Similarly, leaf reflectance properties exhibited a significant difference between individual stress treatments indicating that the hyperspectral sensor data can be used to discriminate RKN-infected plants from drought-stressed plants. Thus, our study reveals that hyperspectral and physiological changes in response to RKN and DS could help diagnose plant health before visual symptoms.

The genetic base for upland cotton (Gossypium hirsutum L.) is narrow for the economically important fiber traits of strength and length. We developed random mated population RMUP‐C5 from 11 parental lines and released seed in 2008. We have now developed 550 recombinant inbred lines (RILs) from this population and evaluated them for fiber properties in eight environments. We report the development and release of seven RILs with improved fiber strength and/or upper half mean length: MS‐RIL‐009 (Reg. no. GP‐1100, PI 698460), MS‐RIL‐037 (Reg. no. GP‐1101, PI 698461), MS‐RIL‐204 (Reg. no. GP‐1102, PI 698462), MS‐RIL‐219 (Reg no. GP‐1103, PI 698463), MS‐RIL‐282 (Reg. no. GP‐1104, PI 698464), MS‐RIL‐303 (Reg. no. GP‐1105, PI 698465), and MS‐RIL‐490 (Reg. no. GP‐1106, PI 698466). Fiber strength and length for the seven lines are as follows: MS‐RIL 009 (384, 30.0), MS‐RIL 037 (369, 31.3), MS‐RIL‐204 (333, 32.5), MS‐RIL‐219 (345, 31.8), MS‐RIL‐282 (295, 31.4), MS‐RIL‐303 (379, 31.4) and MS‐RIL‐490 (318, 33.0), kN m kg^–1 and mm, respectively. Fibers of MS‐RILS 037, 219, and 303 are significantly stronger and longer, fibers of 009 are significantly stronger, and fibers of 204, 282, and 490 are significantly longer than fibers of ‘Acala Ultima’ or ‘Fibermax 966’, the parental lines with the strongest (326–334 kN m kg^–1) and longest (29.3–30.0 mm) fibers. MS‐RIL‐009, MS‐RIL‐037, MS‐RIL‐219, and MS‐RIL‐303 are homozygous for favorable alleles at the A07 strength quantitative trait locus (QTL). All lines except MS‐RIL‐009 are homozygous for favorable alleles at the D11 length QTL.