The primary objective of this work was to generate species-specific information about root architectural responses to variations in inorganic phosphate (Pi) availability at the onset of storage root formation among six sweetpotato (Ipomoea batatas) cultivars. Three Pi levels were used: 0 (low Pi); 0.17 (medium Pi); and 0.34 (high Pi) g/pot triple super phosphate (0N–46P–0K). The check cultivar ‘Bayou Belle’ (BB) consistently showed evidence of storage root formation at 15 days in adventitious roots (ARs) grown across three Pi levels and two planting dates (PDs). Storage root formation was also detected in ‘Orleans’ (OR) and ‘Beauregard’ (BX), but it was less consistent relative to BB. In general, BB had the lowest adventitious root (AR) number relative to the other cultivars, but the magnitudes of difference varied with Pi availability and PD. With the first PD, BX had a 45% higher AR number compared with BB in low Pi conditions; however, there were no differences in the second PD. Within cultivars, BX and Okinawa grown in low Pi showed combined 17% and 24% reductions in primary root length (PRL) relative to roots grown in high Pi. BB had a higher lateral root number (LRN) and lateral root density (LRD) across Pi levels, corroborating prior data regarding the association of these root architectural attributes with the onset of storage root formation. The experimental data support the hypothesis regarding the existence of genetic variation for Pi efficiency in sweetpotato and that some well-documented Pi-efficient root traits like high LRN and LRD are indirectly selected for in-breeding programs that focus on early storage root formation and stable yields across environments.

Phosphorus deprivation (−P) reduced sweetpotato storage root length (SRL) regardless of the presence or absence of a compacted layer (CL). The combination of −P and the presence of a simulated compacted layer (+CL) reduced SRL relative to the P-sufficient (+P) control plants grown without a compacted layer (−CL) by 44% and 40%, respectively, in ‘Bayou Belle’ and ‘Beauregard’ cultivars. In both cultivars, the combination of −P and −CL also reduced SRL by 36% (‘Bayou Belle’) and 28% (‘Beauregard’) relative to the control plants. There was a significant planting date × cultivar effect in the temporal −P studies, with a general trend for SRL reduction with −P at 10-day intervals over a 50-day growing period. −P treatment reduced ‘Bayou Belle’ SRL after 10 days but not after 20 days. In P source plant status studies, the −P/−P treatment (source plant P status/daughter plant P status) was associated with 50% and 48% reduction in SRL in ‘Bayou Belle’ and ‘Beauregard’ daughter plants, respectively, relative to the +P/+P control plants. Taken together, these findings corroborate previous experimental evidence on the role of P in determining root length in other plant species and experimental systems. These experimental findings have practical applications in the management of P in sweetpotato seed and production systems. The results of the current study can lead to follow-up work that validates cultivar-specific P requirements and how such information can be used to optimize P management as it relates to the production of storage roots of consistent length and shape. The methods and approaches used in the current study can be adopted and modified in follow-up investigations that seek to shed light on the precise mechanisms of SRL determination in sweetpotato.

The growing demand for sweetpotato French fry and other processed products has increased the need for producing storage roots of desired shape profile (i.e., blocky and less tapered). Length-width ratio (LW) is the current de facto standard for characterizing sweetpotato shape. Although LW is sensitive and descriptive of some types of shape variability, this index may be inadequate to measure taper and other subtle shape variations. Prior work has shown that surface area (SA) and volume (VOL) are important shape descriptors but current direct measurement methods are tedious, inconsistent, and often destructive. A low-cost three-dimensional (3D) scanner was used to acquire digital 3D models of 210 U.S. No. 1 grade sweetpotato storage roots. The 3D models were imported into Meshmixer, a free software for cleaning and processing 3D files. Processing steps included gap filling and rendering the models water-tight to facilitate VOL measurements. The software includes a tool that enables automatic measurements of length (L), width (W), SA, and VOL. LW and SA-VOL ratio (SAVOL) were subsequently calculated. Separately, a digital caliper was used for manual measurements of L and W. The shrink-wrap method was used to measure SA, and water displacement was used to measure VOL. 3D scanner-based and manual L measurements showed high correlation, whereas VOL was lowest. Principal component analysis (PCA) of 3D scanner-based measurements showed that the first two principal components (PCs) accounted for 96.2% of the total shape variation in the data set, named Ib3D. The first PC accounted for 62.15% of the total variance, and captured variation in storage root shape through changes in VOL, SA, SAVOL, and W. The second PC accounted for 34.4% of the variance, and the main factors were LW and L. Most storage root samples that were classified as processing types were located in the fourth quadrant. The methods described in this work to nondestructively acquire 3D models of sweetpotato also can be adopted for analyzing shape in other horticultural produce like fruits, vegetables, tubers, and other storage roots that meet the specifications for 3D scanning. The data support the hypothesis that knowledge of variables that determine storage root L and W can lead to the development of methods and approaches for enhanced processing product recovery and size assortment for fresh market.

The primary objective of this work was to generate species-specific information about root architectural adaptation to variation in boron (B) availability at the onset of storage root formation among three sweetpotato [Ipomoea batatas (L.) Lam] cultivars (Beauregard = BX; Murasaki = MU; Okinawa = OK). Three B levels were used: 0B (B was omitted in the nutrient solution, substrate B = 0.1 mg·kg−1), 1XB (sufficient B; 0.5 mg·kg−1), and 2XB (high B; 1 mg·kg−1). The check cultivar BX showed evidence of storage root formation at 15 days in 0B and 1XB, whereas cultivars MU and OK failed to show evidence of root swelling. The 1XB and 2XB levels were associated with 736% and 2269% increase in leaf tissue B in BX, respectively, relative to plants grown in 0B. Similar magnitudes of increase were observed in MU and OK cultivars. There were no differences in adventitious root (AR) count within cultivars but OK showed 25% fewer AR numbers relative to BX across all B levels. 0B was associated with 20% and 48% reduction in main root length in BX and OK, respectively, relative to plants grown in 1XB and 2XB. 2XB was associated with a 10% increase in main root length in MU relative to plants grown in 0B and 1XB. 0B was associated with reduced lateral root length in all cultivars but the magnitude of responses varied with cultivars. These data corroborate findings in model systems and well-studied crop species that B deficiency is associated with reduced root growth. These data can be used to further understand the role of cultivar-specific responses to variation in B availability in sweetpotato.

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