As one of the world's most important food crops, potato (Solanum tuberosum L.) has spurred innovation in autotetraploid genetics, including the use of SNP arrays to determine allele dosage at thousands of markers. By combining genotype and pedigree information with phenotype data for economically important traits, the objectives of this study were to (1) partition the genetic variance into additive vs. non-additive components, and (2) determine the accuracy of genome-wide prediction. Between 2012 and 2017, a training population of 571 clones was evaluated for total yield, specific gravity, and chip fry color.Genomic covariance matrices for additive (G), digenic dominant (D), and additive x additive epistatic (G#G) effects were calculated using 3895 markers, and the numerator relationship matrix (A) was calculated from a 13-generation pedigree. Based on model fit and prediction accuracy, mixed model analysis with G was superior to A for yield and fry color but not specific gravity. The amount of additive genetic variance captured by markers was 20% of the total genetic variance for specific gravity, compared to 45% for yield and fry color. Within the training population, including non-additive effects improved accuracy and/or bias when predicting total genotypic value, for all three traits. When six F1 populations were used for validation, prediction accuracy ranged from 0.06 to 0.63 and was consistently lower (0.13 on average) without allele dosage information. We conclude that genome-wide prediction is feasible in potato and will improve selection for breeding value given the substantial amount of non-additive genetic variance in elite germplasm.4

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der et al., 1994). Water soluble carbohydrates directly stabilize aggregates (Angers and Mehuys, 1989) and Soil structural degradation is common in intensively cultivated have been strongly correlated (r ϭ 0.74) with aggregaecosystems due to the depletion of soil organic matter (SOM). We tion (Haynes and Swift, 1990). investigated the mechanisms by which different frequencies of organic amendment application and rotation crops restore C, N, and aggrega-Green manure crops increase soil C inputs, but their tion in gravelly loam soils used for potato production. A single amendeffects on SOM equilibrium and aggregation may occur ment application [FIRST; 22 Mg ha Ϫ1 compost and 45 Mg ha Ϫ1 beef slowly because background levels of soil C are relatively cattle (Bos taurus L.) manure] did not affect total C in 1996 and inhigh and spatially variable (Robertson et al., 1993, 2000). creased it by 28% in 1997 relative to unamended plots (NONE); light Long-term annual compost and manure applications infraction (LF) C accounted for 56% of this increase. Plots in which crease SOM and structure (Sommerfeldt et al., 1988; amendment was suspended for 1 yr (SASP) following 4 or 5 yr of Gilley and Risse, 2000); however, annual applications annual application had more total C in 1996 (28%) and 1997 (46%) are expensive (Araji et al., 2001) and thus not widely relative to NONE. A green manure crop consisting of oat (Avena sativa utilized in Maine. Applying organic amendments less 'Porter'), pea (Pisum sativum 'Trapper'), and hairy vetch (Vicia villosa than annually would be more cost effective if they could Roth) grown in 2-yr rotation with potatoes (Solanum tuberosum L.) reverse the negative effects of potato production. increased soil C in 1997 (25.9 vs. 23.9 g kg Ϫ1), LF properties in 1996 and 1997, and water soluble carbohydrates (WSC) on several sample Minimizing the frequency of organic amendment apdates relative to an oat rotation crop. Large aggregate (2-6.5 mm) plication depends on predicting the number of applicastability in 1996 and 1997 and medium aggregate (1-2 mm) stability tions necessary to halt declines in SOM and structure in 1997 were increased by FIRST relative to NONE. Total soil C was and, once the decline stops and amendments are no more strongly related to medium (r ϭ 0.65 in 1997) and large (r ϭ longer applied, whether the benefits of amendment per-0.51 in 1997) aggregate stability than LF or water soluble carbohydrate sist. Increases in soil C and total aggregation have been fractions. Compost and manure influences occurred rapidly and were reported in potato cropping systems after a single compersistent, demonstrating that annual applications are not necessary post and manure amendment application (Porter et al., to reverse soil degradation. 1999), but relationships between organic matter pools and aggregation still require elucidation. Effects of organic amendments may last for a century or more on Growing year Amendment and

Sugar release from the pedicel tissue of maize (Zea mays L.) kernels was studied by removing the distal portion of the kernel and the lower endosperm, followed by replacement of the endosperm with an agar solute trap. Sugars were unloaded into the apoplast of the pedicel and accumulated in the agar trap while the ear remained attached to the maize plant. The kinetics of "C-assimilate movement into treated versus intact kernels were comparable. The rate of unloading declined with time, but sugar efflux from the pedicel continued for at least 6 hours and in most experiments the unloading rates approximated those necessary to support normal kernel growth rates. The unloading process was challenged with a variety of buffers, inhibitors, and solutes in order to characterize sugar unloading from this tissue.Unloading was not affected by apoplastic pH or a variety of metabolic inhibitors. Although p-chloromercuribenzene sulfonic acid (PCMBS), a nonpenetrating sulfhydryl group reagent, did not affect sugar unloading, it effectively inhibited extracellular acid invertase. When the pedicel cups were pretreated with PCMBS, at least 60% of sugars unloaded from the pedicel could be identified as sucrose. Unloading was inhibited up to 70% by 10 millimolar CaCl2. Unloading was stimulated by 15 millimolar ethyleneglycol-bis(6-aminoethyl ether)-N,N,N',N'-tetraacetic acid which partially reversed the inhibitory effects of Ca21. Based on these results, we suggest that passive efflux of sucrose occurs from the maize pedicel symplast followed by extracellular hydrolysis to hexoses.

This study was conducted to determine if supplemental irrigation and/or application of soil amendments rich in organic matter can improve root growth of potato (Solanum tuberosum L.). Root length density (RLD) and root dry matter production of potato were studied under two levels of supplemental irrigation (nonirrigated check vs. moderate irrigation) and two levels of soil amendments [none vs.