The effects of row spacing and genotypic frequency on the yield of soybean (Glycine max (L.) Merr.) blends were evaluated for use in establishing testing procedures for new blends. In 1969 and 1970, ‘Chippewa 64,’ ‘Hark,’ ‘Corsoy,’ ‘Provar,’ and ‘Amsoy’ were evaluated in all possible two‐component blends at the frequencies 3:1, 1:1, and 1:3, and in all possible three‐component blends in a 1:1:1 frequency. The blends and pure stands were tested for yield in 70‐ and 100‐cm rows.The average yield response of blends to narrow rows was similar to that of pure cultivars. The average yield increase in 70‐cm rows over 100‐cm rows was 9.6% for the two‐component blends, 10.2% for the three‐component blends, and 10.0% for the cultivars in pure stand.Average compensatory responses (deviations of actual blend yields from the weighted means of their component cultivars in pure stand) were similar for both spacings. The average compensatory response was 69 kg/ha or 2.5% for 100‐cm rows and 72 kg/ha or 2.4% for 70‐cm rows.Although row spacing generally did not influence compensatory responses, there were blends that had significant deviations from the expected yield in one spacing but not in the other. Furthermore, the percentage yield differences in two row spacings for a blend could not be consistently estimated from the percentage row‐spacing response of its component cultivars. It seems that whenever possible, the compensatory response of a blend and its yield response to different row spacings should be evaluated by testing the blend per se in the row spacings of interest.In 1971 and 1972, genotypic frequencies in four two‐component blends were varied in 10% increments from 100:0 to 0:100. Compensatory responses of the blends were found to be dependent on genotypic frequency. Maximum yields of the blends generally occurred over a limited range of genotypic frequencies. All blends had their highest yields when the highest yielding cultivar made up at least 70% of the blend.

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Tomato spotted wilt virus (TSWV, family Tospoviridae, genus Orthotospovirus) is a thrips-vectored pathogen that infects lettuce (Lactuca sativa) and many vegetable crops (Kuo et al. 2014, Hasegawa et al. 2022). Another thrips-borne pathogen of lettuce, impatiens necrotic spot virus (INSV, Tospoviridae, Orthotospovirus), was first reported in 2021 in Yuma, Arizona (Hasegawa et al. 2022). Symptoms of both viruses in lettuce are similar and include necrotic spotting, leaf chlorosis and plant stunting (Kuo et al. 2014). Beginning February through April of 2022, lettuce displaying symptoms of orthotospovirus infection was collected from romaine lettuce (var. longifolia) fields in three regions of Yuma County. A total of 96 plants were collected (5 from Tacna on 2/21, 5 from Wellton on 2/21, 15 from Wellton on 3/23, 30 from Tacna on 4/4, 20 from Wellton on 4/4, and 21 from Yuma Valley on 4/4). The area of the fields ranged from 10 to 18 acres, and the percent disease incidence ranged from 0.8% (Tacna on 4/4) to 2.75% (Tacna on 2/21). Thrips vector were present in all fields were symptomatic plants were observed. One leaf disk per plant (8 mm in diameter) was sampled with a cork borer and grounded individually with a micro pestle in a 1.7 ml microcentrifuge tube with 150 ul of Tri-reagent (Molecular Research Center). Total RNA was extracted from each sample using the Zymo Direct-zol-96 kit (Zymo Research). Samples were diluted with water to a ratio of 1:10 after RNA extraction. RT-qPCR was performed in 20 ul reactions with 5 ul of input RNA using the PCR Biosystems qPCRBIO Probe 1-Step Go No-ROX for the cDNA/qPCR master mix. RT-qPCR assays were carried out in multiplex reactions using primers specific for TSWV and INSV, in addition to a lettuce internal control gene (LOC111918243), along with negative controls. Primer and probe sequence details are reported in supplemental Table 1. We used a cycle threshold (ct) < 40 to indicate a positive result for both INSV and TSWV (Chen et al. 2013; Boonham et al. 2002). RT-qPCR successfully amplified INSV in 90 out of 96 samples and TSWV in 8 out of 96 samples. These 8 samples tested positive for both TSWV and INSV, showing that INSV and TSWV co-infected lettuce plants. Thus overall, ∼ 95% of symptomatic plants were infected with INSV alone, and ∼ 8% were co-infected with TSWV and INSV. Amplicons of 4 samples testing positive for TSWV were sent for Sanger sequencing (Eurofins Genomics, Louisville, KY). All were identified as TSWV. One amplicon with TSWV was sequenced for INSV and double infection was confirmed. BLAST results from the NCBI nt database show 100% (138 bp) identity to TWSV (MW519211) for the 4 TWSV amplicons and 99.22% (137 bp) identity to INSV (KX790323) for the INSV amplicon. Sanger sequence data are in the GenBank (accession: OQ685940-OQ685944). Based on RT-qPCR results, all TSWV infected plants were also infected with INSV. INSV may have been introduced to Yuma by infected plants or thrips from lettuce transplants produced in California (Hasegawa et al. 2022). TSWV could have been introduced similarly. To our knowledge, this is the first report of TSWV infecting lettuce in Yuma and the first report of INSV and TSWV co-infecting lettuce. TSWV and INSV infections have remained low since their discovery in Yuma, in part due to effective cultural and chemical management by lettuce growers (Palumbo, 2022). However, an increase in disease incidence and severity in the future could have a significant negative impact on production of romaine lettuce in the region.

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