Assessing the allelotypic effect of two aminocyclopropane carboxylic acid synthase-encoding genes MdACS1 and MdACS3a on fruit ethylene production and softening in Malus

Phytohormone ethylene largely determines apple fruit shelf life and storability.Previous studies demonstrated that MdACS1 and MdACS3a,which encode 1-aminocyclopropane-1-carboxylic acid synthases(ACS),are crucial in apple fruit ethylene production.MdACS1 is well-known to be intimately involved in the climacteric ethylene burst in fruit ripening,while MdACS3a has been regarded a main regulator for ethylene production transition from system 1(during fruit development)to system 2(during fruit ripening).However,MdACS3a was also shown to have limited roles in initiating the ripening process lately.To better assess their roles,fruit ethylene production and softening were evaluated at five time points during a 20-day post-harvest period in 97 Malus accessions and in 34 progeny from 2 controlled crosses.Allelotyping was accomplished using an existing marker(ACS1)for MdACS1 and two markers(CAPS866 and CAPS870)developed here to specifically detect the two null alleles(ACS3a-G289V and Mdacs3a)of MdACS3a.In total,952 Malus accessions were allelotyped with the three markers.The major findings included:The effect of MdACS1 was significant on fruit ethylene production and softening while that of MdACS3a was less detectable;allele MdACS1–2 was significantly associated with low ethylene and slow softening;under the same background of the MdACS1 allelotypes,null allele Mdacs3a(not ACS3a-G289V)could confer a significant delay of ethylene peak;alleles MdACS1–2 and Mdacs3a(excluding ACS3a-G289V)were highly enriched in M.domestica and M.hybrid when compared with those in M.sieversii.These findings are of practical implications in developing apples of low and delayed ethylene profiles by utilizing the beneficial alleles MdACS1-2 and Mdacs3a.

Identification of two QTLs associated with high fruit acidity in apple using pooled genome sequencing analysis

Acidity is a critical component determining apple fruit quality.Previous studies reported two major acidity quantitative trait loci(QTLs)on linkage groups(LGs)16(Ma)and 8(Ma3),respectively,and their homozygous genotypes mama and ma3ma3 usually confer low titratable acidity(TA)(<3.0 mg ml^(−1))to apple fruit.However,apples of genotypes Ma-(MaMa and Mama)or Ma3-(Ma3Ma3 and Ma3ma3)frequently show an acidity range spanning both regular(TA 3.0–10.0 mg ml^(−1))and high(TA>10mgml^(−1))acidity levels.To date,the genetic control for high-acidity apples remains essentially unknown.In order to map QTLs associated with high acidity,two genomic DNA pools,one for high acidity and the other for regular acidity,were created in an interspecific F1 population Royal Gala(Malus domestica)×PI 613988(M.sieversii)of 191 fruit-bearing progenies.By Illumina paired-end sequencing of the high and regular acidity pools,1,261,640 single-nucleotide variants(SNVs)commonly present in both pools were detected.Using allele frequency directional difference and density(AFDDD)mapping approach,one region on chromosome 4 and another on chromosome 6 were identified to be putatively associated with high acidity,and were named Ma6 and Ma4,respectively.Trait association analysis of DNA markers independently developed from the Ma6 and Ma4 regions confirmed the mapping of Ma6 and Ma4.In the background of MaMa,20.6%of acidity variation could be explained by Ma6,28.5%by Ma4,and 50.7%by the combination of both.The effects of Ma6 and Ma4 in the background of Mama were also significant,but lower.These findings provide important genetic insight into high acidity in apple.

AppleQSM:Geometry-Based 3D Characterization of Apple Tree Architecture in Orchards

The architecture of apple trees plays a pivotal role in shaping their growth and fruit-bearing potential,forming the foundation for precision apple management.Traditionally,2D imaging technologies were employed to delineate the architectural traits of apple trees,but their accuracy was hampered by occlusion and perspective ambiguities.This study aimed to surmount these constraints by devising a 3D geometry-based processing pipeline for apple tree structure segmentation and architectural trait characterization,utilizing point clouds collected by a terrestrial laser scanner(TLS).The pipeline consisted of four modules:(a)data preprocessing module,(b)tree instance segmentation module,(c)tree structure segmentation module,and(d)architectural trait extraction module.The developed pipeline was used to analyze 84 trees of two representative apple cultivars,characterizing architectural traits such as tree height,trunk diameter,branch count,branch diameter,and branch angle.Experimental results indicated that the established pipeline attained an R^(2)of 0.92 and 0.83,and a mean absolute error(MAE)of 6.1cm and 4.71mm for tree height and trunk diameter at the tree level,respectively.Additionally,at the branch level,it achieved an R^(2)of 0.77 and 0.69,and a MAE of 6.86 mm and 7.48°for branch diameter and angle,respectively.The accurate measurement of these architectural traits can enable precision management in high-density apple orchards and bolster phenotyping endeavors in breeding programs.Moreover,bottlenecks of 3D tree characterization in general were comprehensively analyzed to reveal future development.